总第270期2018年第6期H E B E I M E T A L L U R G YTotal No. 270 2018 , Number 6超低碳IF热轧带钢表面混晶的分析与控制田秀刚12，冯晓勇2，宋晓娟3(1.华北理工大学冶金与能源学院，河北唐山063009;2.河钢集团唐钢公司技术中心，河北唐山063016;.唐钢不镑钢有限责任公司，河北唐山063105)摘要：厚度多4.0m m热乳超低碳IF带钢表面存在混晶现象，显微组织观察发现混晶厚度约占钢带总厚度的3%〜10%。
分析认为，混晶主要由加热温度、终乳温度、中间坯厚度和工艺润滑控制不当导致的。
将加热温度由1040 °C提高到1050 °C，终乳温度由900 °C提高到930 °C，中间坯厚度由36 m m增加到45 m m，工艺润滑由50 m l/m in增加到60 m l/m in后，晶粒度等级差距缩小1级，混晶现象得到明显改善。
关键词：超低碳I钢；带钢；表面混晶；分析;控制中图分类号：TG335.5 文献标识码：B 文章编号：1006 - 5008 (2018 ) 06 - 0047 - 03doi:10. 13630/j. cnki. 13 - 1172.2018.0612ANALYSIS AND CONTROL OFSURFACE MIXED CRYSTAL INULTRA - LOW CARBON HOT STRIP STEELT ia n X iu g a n g1,2，F e n g X ia n y o n g2，S o n g X ia o ju a n3(1. School of metallurgy and energy of North China University of Science and Technolo bei ,063009；2. Tangshan branch technology center of HBIS Co. , Ltd，Tangshan , Hebei , 063016；3. Tang-steel stainless stee C o.，Ltd，Tangshan，Hebei，063105)Abstract：Surface mixed crystal phenomenon existed in ultra -low carbon hot strip steel larger than 4. 0 mm. Microstructure observation showed that the coarse - grain thickness is 3% to 10% of thewhole strip steel thickness. It is believed that the mixed crystal structure was caused by heating temperature，finish rolling temperature，transfer - bar thickness and technique lubrication. The mixed crystal structure wasobviously improved with the grain grade difference less than 1after the heating temperature from 1040 C to 1050 C, the finish rolling temperature increased from 900 C to 930 C , the transfer - barthickness increased from 36 mm to 45 mm and the technique lubrication adjusted slightly from 50 ml.Key Words：ultra - low carbon IF steel；strip steel ；surface mixed crystal ；analysis ；control0 引言热轧带钢显微组织的均勻性对其强度和塑性有 很大的影响，均勻细小的显微组织在变形过程中晶 界协调性较好，有助于变形能力的提高，而一旦出现 混晶现象则会导致塑性显著下降[1]。
Review of mechanical behavior and microstructure ofMagnesium alloyAbstract: Magnesium alloys are introduced in this article. The mechanical behavior and microstructure of Magnesium alloy are discussed in the review. The characteristics of Magnesium alloy are researched by researchers. The mainly deformation mechanisms of Magnesium alloy are slip and twinning which determined by the grain structure of magnesium. There is a great relationship between mechanical properties and microstructure of Magnesium alloy. And there are many ways to improve the mechanical properties of Magnesium alloy by grain refinement. Superheating, carbon inoculation, the elfinal process, control of impurity level, zr addition, other element additions, rapid solidification and physical grain refining are illustrated in this review, and all those can be used to refine the grain of Magnesium alloy.Key words: Magnesium alloy; Microstructure; Deformation; Strength; Grain refinement 1.IntroductionMagnesium alloys have been received a great attention as light-weight structure materials because of specific strength, high stiffness, good damping capacity andeasy-recycling and so on[1]. Magnesium is the lightest structural metal with a densityof only 1.738 g/cm3 at 20℃[2]. For engineering applications, magnesium is usually strengthened by alloying mechanism; it can be alloyed with other alloying elements such as aluminum, zinc, manganese, zirconium and rare earth.[3]Contain of various ingredients of magnesium alloy are largely studied by scientific researchers. Magnesium alloys containing rare earth elements are known to have high specific strength, good creep and corrosion resistance up to 523K. The addition of SiC ceramic particles strengthens the metal matrix compo site resulting in better wear and creep resistance while maintaining good machinability [4]. Kawamuraet al.[5] have developed a RS P/M Mg-1Zn-2Y alloy, and this alloy shows excellent mechanical properties. Liu et al.[6] investigated the thixoformability in alloys based on the Al–Si–Cu and Al–Si–Cu–Mg systems using MTDATA thermo-dynamic and phase equilibrium software combined with the MTAL database. Criteria for thixoformability are identified and a range of alloy compositions based on Al–Si–Cu andAl–Si–Cu–Mg evaluated in relation to these criteria. Birol[7] studied the thixoformability of AA6082 aluminum alloy reheated from the as-cast and extruded states, respectively. The thixoformability of the as-cast alloy was inferior with respectto that from the extruded material. Camacho et al.[8] studied the wrought alloy compositions amenable to semi-solid processing, using a commercial software package MTDATA, NPL alloy solution database MTSOL and SGTE substance database. Commercial thixoforming is generally based on conventionalaluminum-based casting alloys such as A356 and A357, which provide high fluidity and good castability[9].2. DeformationFor magnesium alloys, slip and twinning, are well known to be two major orientation-dependent deformation mechanisms. Both basal slip (with a 1/3〈112＿0〉Burgers vector) and non-basal slip (e.g. first-order {101＿0} prism slip and {101＿1} pyramidal slip) systems have been reported extensively. Moreover, as all the slip systems mentioned above cannot produce plastic deformation parallel to thec-direction, twinning usually plays an important role in the plasticity of these materials[10].Twinning and slip in hexagonal close-packed structures have been extensively studied using molecular dynamics. Barrett et al.[11] utilized MD simulations to explore slip and twin nucleation mechanisms and their sensitivity to Schmid and non-Schmid stresses by first loading a defect-free crystal having full periodic boundary conditions under various uniaxial loading directions.The deformation temperature is an important factor to Magnesium. Li et al.[12] investigated the effects of deformation temperature on microstructure and mechanical properties of AZ80 magnesium alloy. The mechanical properties and microstructure were carried out in Gleeble-1500 thermal simulation experiment and optical microscope. The extrusion deformation, dynamic recrystallization had taken place in all the deformation samples, grains were thinner than before deformation. The reasonable deformation process can make the dynamic recrystallization organization of grain smaller and obtain higher strength. The best deformation temperature was about 360 degrees C to 390 degrees C to AZ80 magnesium alloy [12]. Xu et al. discussed the effect of microstructure and texture on the mechanical properties of the as-extruded Mg–Zn–Y–Zr alloy specimens at room temperature [13].Lu et al. [10] focuses on the monotonic and cyclic behavior of a high-pressure die cast magnesium AM60B alloy. The mechanical results are discussed with respect to the microstructure in terms of clusters of pores, grain size and theorientation-dependent activation of different deformation mechanisms.Shi et al. [14] investigated the compression of a semi-solid Zn-Al alloy disc as it is often used as a filler metal to braze aluminum alloys and their composites. Three different size discs were used with height-to-diameter ratios (hid) of 0.6, 0.3 and 0.1. Stress-strain curves were obtained during disc compressions. The maximum stress obtained during the compressions increased with a decrease in disc size (hid). Hagihara et al. [15] investigated the influence of a change in the stacking sequence of the close-packed plane in a Mg12ZnY long-period stacking ordered (LPSO) phase on its mechanical properties. A 14H-typed LPSO-phase crystal was fabricated by annealing a directionally solidified (DS) crystal with a 18R-typed LPSO-structure at 525 degrees C for 3 days, and the temperature dependence and orientation dependence of the yield stress were examined via compression tests. (0001)< 11 (2) over bar0 > basal slip was identified as a dominant deformation mode, and deformation kink bands were formed under compression in the case of suppression of basal slip motion. The deformation mechanism of the 14H-typed LPSO-phase is almost similar to that of the 18R-typed LPSO-phase, even though a slight differencewas observed at temperatures above 300 degrees C.3. StrengthThere many factors that affect strength of magnesium alloy. Accordingly, considerable approaches have been explored to attain higher strength and ductility on Magnesium alloys in recent years. Grain refining is an effective procedure for achieving high strength at RT together with possible superplastic forming capabilities at elevated temperatures for many face-centered cubic (fcc) metals[16].Severe plastic deformation will effectively result in significant grain refinement in many metals and this may be achieved using procedures such as equal-channel angular pressing (ECAP), accumulative rolling bonding (ARB) and high pressure torsion[17].In general, the strength and ductility of materials processed by ECAP cannot be readily enhanced simultaneously. Recently, several strategies were proposed to achieve the relatively high uniform elongation in those strong UFG fcc metals [18]. Wang et al. pro-posed that the UFG metals and alloys can exhibit a combination of high strength and good ductility by designing their grain size to form a bimodal microstructure in pure copper. Zhao et al. [19] reported that a large fraction of equilibrium HAGBs and low dis-location density could improve the toughness and the uniform elongation of UFG materials by imparting excessive processing plastic strain. Lu et al.[10] suggested that the strength and uniform elongation could be simultaneously ameliorated in the UFG Cu by inducing nanotwins. In all theabove-mentioned toughening strategies, the UFG microstructures can provide the high strength; while different microstructures (duplex grain sizes, equilibrium HAGBs and nano-twins and stacking faults) contribute to the ductility by improving thestrain-hardening ability[20].The microstructure, texture and tensile properties of this magnesium alloy before and after ECAP were systematically investigated at RT and the relationship between microstructure and mechanical properties was elucidated through detailed analysis[21].A particle-strengthened magnesium alloy, Mg–12Gd–3Y–0.5Zr, has been processed successfully by ECAP. The microstructural evolution was studied systematically by TEM. The relation-ship between strength and elongation was discussed in termsof its BU microstructure. The following conclusions may be drawn: (1) After four-passes ECAP, a BU microstructure, containing the matrix grains and the second-phase particles with the average sizes of 490 nm and 290 nm, respectively, was obtained.(2) The tensile strength and elongation of the Mg alloy with the BU microstructure can be simultaneously increased at RT.(3) The tensile strength increment of the BU microstructure can be mainly attributed to the combined influences of matrix grain refinement and enhanced dispersion strengthening. While the tensile ductility increment of the BU microstructure is closely related to the formation of profuse microscale shear bands.(4) The fracture mechanisms are attributed to debonding the inter-face between particle and matrix grain for the samples E0 with eutectic-phase particles at grain boundary and the linkage of microscale shear bands for samples E4 with BU microstructure[21].4. MicrostructureAlthough Magnesium alloys have outstanding strength/weight ratio, the important disadvantages of Magnesium alloys are low strength and low ductility compared with the other competitive structural materials such as Al and steel. It is well known that a finer grain size may contribute synchronously to the strength and ductility [3]. A good mechanical behavior of Magnesium alloy can be obtained through changing its microstructure. The mainly method can get excellent mechanical behavior is grain-refining method.Fine grain microstructure favors uniform deformation and improves isotropic mechanical properties of the materials with hexagonal close-packed (hcp) structure [22]. It is also well-known that, the microstructure prior to forging or extrusion, i.e. the solidified structures of an ingot, has a significant impact on the subsequent forging properties [22].Many techniques are available to achieve grain refinement. Among them, the post-solidification techniques involve deformation processing and severe plastic deformation techniques. Among the solidification processing techniques, rapid quenching, particle inoculation (chemically assisted), and use of physical means have shown promise.Nowadays, there have been various grain-refining methods developed for changing the microstructure of Magnesium alloy, such as superheating, carbon inoculation, the elfinal process, control of impurity level, zr addition, other element additions, rapid solidification and physical grain refining.4.1. Superheating methodThe superheating process was originally described in a British patent granted in 1931[23]. Aluminum bearing magnesium alloys benefit from high-temperature treatment in terms of grain refinement. This high-temperature treatment is usually termed as superheating and the process involves heating the melt to a temperaturewell above the liquidus of the alloy often in the range 453K to 573 K for a short time, followed by rapid cooling to, and short holding at, the pouring temperature. Although the grain refinement efficiency of superheating is subjected to many factors, there are some basic characteristics of this technique. Starting with, a significant grain refinement response can only be achieved in Mg-Al alloys with a minimum addition of Mn/Fe content. Then, a specific temperature range above the pouring temperatureis required to maximize the grain refining effect. Finally, rapid cooling from the overheating temperature to the pouring temperature and the short holding time are also crucial requirements to produce fine grains.A model has been proposed on the basis of the recent understanding of the grain refinement of both high purity and commercial purity Mg–Al alloys[23]. It simply involves heating a molten magnesium alloy to a temperature well above the liquidus of the alloy, holding it for a required period, and then cooling rapidly to the required pouring temperature. Figure 1 illustrates three different superheating cycles. Although extensive investigations have been carried out and a number of hypotheses have been proposed since the 1930s, the grain refinement mechanisms remain unclear.Understanding of the controlling mechanism will help foster the development of an effective grain refiner for Mg–Al alloys. This work proposes a new hypothesis for the grain refinement of magnesium alloys by superheating on the basis of the recent developments in grain refinement of magnesium alloys. The model is applied to elucidating the various phenomena observed about superheating. Schematic of typical temperature profiles during a superheating process of Mg–Al alloys are illustrated Fig.1[23].Fig. 1 Schematic of typical temperature profiles during a superheating process ofMg–Al alloys. The superheat temperature T sh is usually in the range of 850–900 °C. The pouring temperature T p is generally around 720 °C. Three different cooling conditions are shown: (1) rapid cooling from T sh to T p with a short holding time before casting; (2) rapid cooling from T sh to T p, but a lengthy holding at T p before casting; and (3) slow cooling from T sh to T p.[23]4.2. Carbon inoculationCarbon inoculation, which developed at the end of World War II, is another major grain-refining process for Mg-Al based alloys. This method is featured with low operating temperature, less fading, short processing time and crucible wear, and therefore favors practical applications [3].As for the grain refinement mechanism of carbon inoculation, the most commonly accepted theory is that Al4C3 particles formed in the Mg-Al melt act as effective nuclei for the Mg grain solidification. It is approved by the fact that the effective addition of carbon inoculant is only confined to Al-containing magnesium alloys. However, no experimental evidence that the Al4C3 particles act as the heterogeneous nuclei of primary α-Mg is observed by micrographs till now. Theapplication range of carbon inoculation method is limited because the grain refining mechanism cannot be understood clearly[24].In recent studies, some researchers proposed that the presence of Mn is necessary to form the heterogeneous nuclei for grain refinement of Mg-Al alloys. Therefore, the role of Mn in grain refinement of Mn containing Mg-Al based alloys should be further investigated to understand the grain refinement mechanism of carbon inoculant treatment. In this work, a novel MgCO3 contained carbon inoculant mixture was developed for grain refinement of AZ91D alloy. The grain refinement process and mechanism of this inoculant on Mg-Al alloy under different processing conditions were investigated experimentally[24].Carbon black is an easily available and inexpensive form of carbon that has nano size morphology. Present work investigates the inoculation potency of these nano particles in Mg–Al alloy melts [25]. It is noted that carbon inoculation grain refinement is only applicable to aluminum-containing magnesium alloys. Accordingly, some researchers put forward that the high-purity carbon powder or the magnesite particles should be added to replace harmful hexachloroethane in the carbon inoculation treatment.4.3. The Elfinal processThe Elfinal process has been invented by the metallurgists of a pioneering German magnesium company based on the hypothesis that iron particles can act as nucleation sites for magnesium grains[26]. It has been reported that Mg-Al-Zn alloys (Al: 4 to 8.5 pct; Zn: 0.5 to 3 pct; no other elements have been mentioned) can be grain refined by additions of 0.4 to 1.0 pct of anhydrous FeCl3 at a temperature range of 1013 K to 1053K. Though the approach has worked satisfactorily in terms of grain refinement but the inventors fail to convince other metallurgists about the mechanism behind it. Different mechanisms have been subsequently proposed. It has been suggested that Fe- containing intermetallic particles or aluminium carbide (Al4C3) particles are possibly the nucleants. According to Emley, hydrolysis of FeCl3 in the magnesium melt gives rise to copious hydrogen chloride (HCl) fumes, which then attack steel crucibles to liberate some carbon into the melt. The other major hypothesis proposed is that Mg grains nucleate on Fe-Mn-Al particles. A detailed examination of this process has been performed to clarify a number of key issues (i) whether Fe is a grain refiner or an inhibitor for Mg-Al alloys (ii) whether iron only grain refines Mg-Al alloys that contain Mn and (iii) the mechanism by which the Elfinal process works[27].For the work stated above, sublimed high-purity magnesium ingots (99.98%) and commercial high-purity aluminium ingots (99.999%) have been used to prepare high-purity Mg-3%Al and Mg-9%Al alloys. Melting has been conducted in an electrical resistance furnace under a protective cover gas of 1.0%SF6 in 49% dry air and 50% CO2.Aluminums titanite crucibles have been used for the reason that they are free of carbon. Anhydrous FeCl3 has been plunged into the melt at 1023 K. Cone sampleshave been taken from the top of the melt using a boron nitride coated cone ladle (Ø 20mm x Ø 30mm x 25 mm), 10 min following addition of FeCl3. No stirring has been applied in each test. The average grain size of each cone sample has been measured from the central region of a longitudinal section of the cone cut through the axis[3].4.4. Control of impurity levelAn interesting observation that has been made about the grain refinement of Mg-Al type alloys is the influence of the source magnesium impurity level. This native refinement in Mg-Al type alloys is said to have occurred when the native grain size is finer than that of commercial purity alloys. It is unclear whether native grain refinement of high purity Mg-Al alloys is conditional upon the C and Al contents. The difficulty of clarifying the role of carbon lies in the difficulty of how to accurately determine a trace level of carbon in magnesium alloy.In a recent work done to understand the mechanism of native grain refinement in Mg-Al alloys, the raw materials used are high-purity aluminium, commercial purity zinc and calcium, and two different sources of magnesium metal, which include sublimed high purity magnesium(99.98%) and commercial purity magnesium(99.7%).It has been found that, Mg-Al alloys with the same basic composition, but made of different sources of magnesium metal, showed an obvious difference in grain size, which is represented in Fig.2. High purity alloys consistently have proved a finer grain size than commercial purity alloys in all cases across the composition range0.5-9%Al. Fig. 3 are microstructural observations corresponding to Mg–9%Al alloys.Fig.2 Effect of source magnesium purity on the grain size of Mg-Al alloys[28].Fig.3. Grain structures in Mg–9%Al alloys made of (a) commercial purity magnesium metal, average grain size (AGS): 200 μm, and (b) high purity magnesium metal, AGS=140 μm.Native grain refinement was observed exclusively in high purity Mg–Al alloys. Mg–Zn and Mg–Ca alloy systems do not show native grain refinement, but rather native grain coarsening in the high purity alloys. The grain size of Mg–9%Al alloys was found to increase with an increase in the proportion of commercial purity magnesium metal used in making these alloys, i.e. impurity level, in the experimental range from 0% to 100% commercial purity magnesium.4.5. Zr addition and Other element additionsZirconium is a potent grain refiner for pure magnesium and is ineffective in magnesium alloys that contain Al, Mn, Si, Fe, Ni, Co, Sn and Sb as zirconium forms stable compounds with these elements[29]. When added to these alloys, where the maximum solubility of zirconium in molten pure magnesium at 927 K is ~ 0.45%, Zr can readily reduce the average grain size to about 50ìm from a few millimeters at normal cooling rates. Moreover, well-controlled grain refinement by Zr can lead to formation of nearly round or nodular grains, which further enhance the structural uniformity of the final alloy. This exceptional grain-refining ability of Zr has led to the development of a number of commercially important magnesium alloys including a few recently developed sand-cast creep resistant magnesium alloys that are aimed at automotive applications such as transmission cases and engine blocks[26]. The most characteristic feature of the microstructure of a magnesium alloy containing more than a few tenths per cent soluble Zr is the Zr-rich cores that exist in most magnesium grains. These Zr-rich cores are usually less than 15 P m in size at normal cooling rates. They are believed to be the products of peritectic solidification. In order to know the mechanism of grain refinement by Zr and capitalize on the grain-refining ability of Zr, it is required to understand the characteristics of these Zr- rich cores[30].At present grain refinement of these alloys is commercially carried out by the addition of a Zr- rich Mg-Zr master alloy, which contains Zr particles ranging from sub-micrometer to 50 Pm in size. It has been found that grain refinement of magnesium alloys by Zr is dictated by both soluble and insoluble Zr contents. However, Zr particles settle very faster in molten magnesium due to the significant difference between the densities of Zr and molten magnesium[31]. As a result, the average grain size increases obviously with increasing residence time of the melt prior to pouring. Moreover, once the Zr particles that are released from a Mg-Zr master alloy added to the melt settle to the bottom of the alloying vessel, little dissolution can be expected of these particles in the absence of stirring. Hence, the particle size distribution in a Mg-Zr master alloy can be understood mainly from a settling point of view rather than from the nucleation point of view. The identification of effective nucleant particles is commonly based on the assumption that after nucleation on any particle added to the melt latent heat release will decrease the likelihood of nucleation on neighbouring particles, which subsequently will be pushed to grain boundaries or into the interdendritic spaces[32]. Therefore, an effective nucleant particle is always expected in the central regions of grains. Compared to the grain refinement of mostother alloys, where it is usually difficult to find a large number of nucleant particles on polished sections, Zr-rich particles that have played a role as nucleation centers in a magnesium alloy can be readily distinguished using a SEM in the BSE image mode, due to the characteristic particle-core structures that form during solidification. Certainly, any information about the size distribution of these particles will help understand the potency and efficiency of Mg-Zr master alloy grain refiner, providing an important basis for improving the design of a grain refiner[33].In magnesium alloys, Zr element has relatively larger GRF value compared with other elements, so it possesses stronger grain refining ability as mentioned previously. Similar to Zr, Ca, Sr and Sb can be effective additions for refining grain size of magnesium alloys[34].4.6. Rapid solidificationIt is well known that rapid solidification processing (RSP) is an important grain refinement method[35]. There are two basic techniques for rapidly solidifying melts: substrate quenching and atomization. Substrate quenching refers to the solidification of the melt against one or two surfaces at a lower temperatures (e.g. room temperature, or near liquid nitrogen)[3]. Substrate quenching includes thermal spray methods,melt-spinning technique, planar flow casting, copper mold casting, twin rolling etc. Atomization is a process of breaking up a molten stream of liquid into small spheres by using gas et. Gas atomization includes high pressure and centrifugal gas atomization et. In substrate quenching, rapid solidification is achieved by increasing the rate of heat extraction and in atomization by increasing the amount of undercooling before nucleation. An average grain size of 0.2- 3 µm can be achieved in the rapid solidification of Mg alloys, and the rapidly solidified Mg-Al-Zn system presented an outstanding ultimate tensile strength of about 500 MPa[5].Besides microstructure refinement, RSP can effectively extend solid solubility in magnesium, for example 1.5 times for Mg-Ag and about 1,000 times for Mg-Ba alloys. The combination of grain refinement and solid solution hardening effect makes RSP a suitable technique for enhancing the mechanical properties and corrosion resistance of Mg alloys[36]. To fabricate structural components, subsequent thermal mechanical processing (e.g. extrusion, forging or rolling and consolidation) is necessary. Depending on the working temperature and processing rate, such hot working significantly impacts the structure of the as-solidified Mg alloys. It should be pointed out that RSP of magnesium alloys poses critical challenges due to the high chemical reactivity of magnesium[37].4.7. Physical grain refining methodsPhysical grain refining methods involve promoting nucleation, dispersion and multiplications of solidified crystals under mechanical force or external physical field without any further chemical additions. Physical grain refinement generally targets creating a favorable condition for nucleation and nuclei survival or breaking thesolidified crystal structures[3].The creation of an ideal condition for nucleation and ensuring high nuclei survival has been employed as a physical grain refinement strategy in the present investigation[38]. Consequently, physical grain refinement increases effective nucleation by tailoring the solidification conditions without necessitating the addition of inoculants. Casting near the liquidus temperature has been known to promote fine equiaxed microstructure. There has been significant controversy in explaining the columnar to equiaxed transition in castings without grain refiner addition. In a comprehensive overview, Hutt and StJohn have discussed the five major available theories and critically assessed the applicability of the proposed mechanisms. It has been concluded by the authors that all proposed mechanisms or a combination of them may be operative depending on the alloy composition, casting conditions or the types of nucleating substrates present[39]. A similar comprehensive analysis of CET and the plausible mechanisms have been discussed by Flood and Hunt. Both of these reviews suggest that in the absence of grain refiner (where constitutional supercooling driven nucleation is important), big bang (also known as free chill crystal or wall mechanism) and dendrite detachment mechanisms are the primary contributors to the creation of equiaxed grains. During low superheat casting the convection associated with the mould filling remains strong as solidification commences. Although it is argued that deformation or melting of the dendrite arms is promoted by the fluid flow, the big bang mechanism becomes progressively important as the melt superheat is reduced[40].5. SummaryThe mechanical behavior of Magnesium alloy has relationship with its microstructure. So it can enhance its deformation ability through refining grain of Magnesium alloy in microstructure, which fine grain size can result in structural uniformity and enhance the mechanical properties, hence improving the service performance of the products. For Magnesium alloys, many grain refinement methods have been developed, but their refining mechanism are still unclear. For example, as the effective grain refinement method, there still is debate in the heterogeneous nuclei for superheating and carbon inoculation of aluminum-containing magnesium alloys. Further investigations are needed for a more comprehensive understanding of the grain refining mechanism, and to develop reliable commercial grain refiners or novel grain refinement processes.References[1] LIU K, MENG J A. Microstructures and mechanical properties of the extrudedMg-4Y-2Gd-xZn-0.4Zr alloys [J]. J Alloy Compd, 2011, 509(7): 3299-3305.[2] ANILCHANDRA A R, BASU R, SAMAJDAR I, et al. Microstructure and compressionbehavior of chip consolidated magnesium [J]. J Mater Res, 2012, 27(4): 709-719.。
