Effect of specific pressure on microstructure and mechanical properties of squeeze casting ZA27 alloy

The effect of specific pressure on the microstructure and mechanical properties of ZA27 squeezed castings with high height-to-thickness ratio was studied. The results of DTA and SEM show that at high specific pressure the eutectic reaction of squeeze casting ZA27 alloy is restrained, and the final solidified structure is (η+ε) phases instead of eutectic phase (β+η+ε). At the same time, the primary reaction is promoted in squeeze casting ZA27 alloy solidified at high pressure, and the fine microstructure is obtained with the increase of pressure. Al and Cu elements are homogeneously distributed in matrix of squeeze casting ZA27 alloy. The homogenously distributed high-density fine ε phase can effectively hinder dislocation motion, and then the strength and plasticity of squeeze casting ZA27 alloy are increased.     

Effect of mold temperature and casting dimension on microstructure and tensile properties of counter-gravity casting Ti-6Al-4V alloys

The cast Ti-6Al-4V alloy bars with different section sizes were fabricated by investment casting at counter-gravity condition with the mold temperatures of 300 °C and 650 °C, respectively. The microstructure of the alloy was observed by means of OM and SEM, and the effect of mold temperature and casting dimension on tensile properties was studied. Results show that equiaxed grains are obtained regardless of the casting dimension. β grain size tends to increase with an increase in mold temperature. Hot isostatic pressing of the alloy was carried out for tensile properties' comparison. Room temperature tensile test results show that Ti-6Al-4V alloy produced via counter-gravity casting has good balance of strength and ductility after hot isostatic pressing(HIP). The alloy shows higher ductility due to the elimination of porosity. In both cast and HIP status, the tensile strength is inclined to decrease with an increase in mold temperature, while the ductility is prone to slightly increase. Both the strength and ductility tend to decrease with an increase in the casting dimension.     

Microstructure and mechanical properties of AZ91D magnesium alloy by expendable pattern shell casting with different mechanical vibration amplitudes and pouring temperatures

To refine the microstructure and improve the mechanical properties of AZ91 D alloy by expendable pattern shell casting(EPSC),the mechanical vibration method was applied in the solidification process of the alloy.The effects of amplitude and pouring temperature on microstructure and mechanical properties of AZ91 D magnesium alloy were studied.The results indicated that the mechanical vibration remarkably improved the sizes,morphologies and distributions of the primaryα-Mg phase andβ-Mg17 Al12 phase,and the densification and tensile properties of the AZ91 D alloy.With an increase in amplitude,the microstructures were gradually refined,resulting in a continuous increase in mechanical properties of the AZ91 D alloy.While,with the increase of pouring temperature,the microstructures were continuously coarsened,leading to an obvious decrease of the mechanical properties.The tensile strength and yield strength of the AZ91 D alloy with a vibration amplitude of 1.0 mm and a pouring temperature of 730℃were 60%and 38%higher than those of the alloy without vibration,respectively.     

EFFECT OF ANNEALING ON DAMPING CAPACITIES OF AS-CAST ZA27 ALLOY

1. Introduction Because ZA27 alloy possesses excellent mechanical properties and high damping capacities, it is widely used in industries. ZA27 alloy has good castability and can be easily cast into various castings by permanent mold casting. The solidification of ZA27 alloy in the permanent mold can be considered to be a nonequilibrium process, and thus the supersaturated aluminum-rich ! phase and unstable copper-rich phase may also be found in the solidified ingot. Those nonequilibrium pha…     

Microstructure and mechanical properties of ZA62 based magnesium alloys with calcium addition

As-cast microstructure and mechanical properties of Mg-6Zn-2Al-0.3Mn (ZA62) alloys with calcium addition were investigated.The as-cast microstructure of the base alloy ZA62 consists of the α-Mg matrix and eutectic phase Mg51Zn20.The Mg51Zn20 eutectic was gradually replaced by MgZn phase and Mg32(Al,Zn)49 phase when calcium is added into the base alloy.Further addition of calcium leads to the increase of grain boundary phases and formation of a new quaternary Mg-Zn-Al-Ca eutectic compound.In comparison with the base alloy,the increase of calcium addition to the base alloy results in the reduction of both strength and ductility at ambient temperature,but increase at elevated temperatures due to the thermal stability of Ca-containing phases.At elevated temperatures,the creep resistance of ZA62 based alloys containing calcium is significantly higher than that of AZ91 which is the most commonly used magnesium alloy.     

Preparation of submicrocrystal Al-Ti-B master alloy and its influence on microstructure and properties of AZ91D

To improve the mechanical properties of AZ91D magnesium alloy,the submicrocrystal Al-Ti-B master alloy was prepared with copper mold inject casting method,and the influence of submicrocrystal Al-Ti-B master alloy on the microstructure and mechanical properties of AZ91D was investigated.Results show that,the distribution of Ti B_2 phase in submicrocrystal Al-Ti-B alloy is even and disperse,and the average size of Ti Al_3 phase is reduced from 10-30μm to～1μm.The properties of AZ91D refined with submicrocrystal Al-Ti-B master alloy are better than that with coarse-grained Al-Ti-B master alloy without copper mold inject casting.The tensile strength,elongation and Brinell hardness of AZ91D are increased by 10.6%,25%and 18.1%,respectively.Therefore,refinement of AZ91D with submicrocrystal Al-Ti-B that is obtained by copper mold inject casting is an effective method to improve its mechanical properties.     

Effects of minor amounts of scandium on microstructure and mechanical properties of ZA27 alloy

The influences of minor amounts of scandium on the microstructure and mechanical properties of as-cast ZA27 alloy have been experimentally investigated. The experimental results show that as far as the Sc addition is individually concerned, the refinement result of the as-cast ZA27 alloy with 0.5wt.%Sc addition is comparatively better. After alloying with minor amounts of Sc, the coarse dendrites of the ZA27 alloy are refined and transformed into the uniform and small equiaxed grain microstructure; also the eutectics among the grain boundaries become finer. The test results of mechanical properties show that the tensile strength and hardness of the as-cast ZA27 alloy containing 0.5wt.%Sc approach 495 MPa and 120.2 HB, increase by 28.5% and 33.1%, respectively, compared with those of the ZA27 alloy with no addition of Sc element, while the elongation of the alloy is improved to 7.6% from 2.7%. The SEM, EDAX and XRD analyses show that in the ZA27 alloy, the trace element Sc combines with AI to form the square AI3Sc phase particles, which serve as heterogeneous nuclei, facilitating the refinement of the microstructure and the improvement of the mechanical properties of the alloy.     

Microstructure and tensile properties of thixo-diecast AZ91D magnesium alloy

The thixo-diecasting （TDC） process is the combination of semi-solid billet preparation technology and die casting technology. The TDC process not only keeps the characteristics of thixo-forming but also has high efficiency and low cost. In the present work, the microstructures and mechanical properties of an AZ91D magnesium alloy prepared by the thixo-diecasting （TDC） process were characterized in as-cast condition. The TDC alloy produced exhibits a unique microstructure containing a-Mg solid solution and/3-Mg~TAI~2 intermetallic compound, and there are some small droplets and a small gray globule with eutectic structure in the primary a-Mg grains. The ultimate tensile strength and elongation of the TDC alloy also increase in comparison with other processes, such as thixocasting. Fracture surface observation shows that a crack mainly originates from the brittle fracture of the eutectic phases. The deformation of ductile a-Mg phase provides the TDC alloy with the main strain.     

Performance of digital patternless freeze-casting sand mould

Digital patternless freeze-casting technology is a new approach for obtaining frozen sand moulds using digital milling technology.The change law of tensile strength and air permeability of frozen sand moulds (100-mesh and 200-mesh silica sand,and zircon sand moulds) under different freezing temperatures and water contents was studied.Results show that with the decrease of freezing temperature and the increase of water contents,the tensile strength and air permeability of the sand moulds are gradually improved.Meanwhile,computed tomography technology was used to characterize the shape and size of the water film between the sand particles mixed with 4wt.% water.The results show that in silica sand moulds,the form of water film is lumpy,and 200-mesh silica sand moulds have more water films and higher proportion of small-sized water films than 100-mesh silica sand moulds,while in zircon sand moulds,the form of water film is membranous.At the same freezing temperature and water content,the tensile strength of zircon sand mould is the highest,and 100-mesh silica sand mould is the lowest.A comparative solidification experiment of A356 aluminum alloy was carried out in frozen sand mould and resin sand mould.The results show that the primary α-Al phase appears in the form of equiaxed and eutectic silicon phase is needle-like in freezing sand mould casting,but the primary α-Al phase grows in the form of dendrites,and the eutectic silicon phase is coarse needle-like in the resin sand mould casting.The difference of microstructure is caused by the different cooling rate.The cooling rate of A356 aluminum alloy in frozen sand mould is higher than that in resin sand mould.     

Process Parameter Optimizing and Studies on Microstructure and Properties of AZ31 Alloy Prepared by Semisolid Rolling Process

A novel continuous semisolid rolling process for producing AZ31 alloy strip was developed. The process parameters were optimized, and microstructure and properties of AZ31 alloy prepared by the process were studied. The results reveal that primary grains of the strip become coarse, and the grain structure transforms from round shape to dendrite with the increment of casting temperature gradually. Eutectic phase fraction and primary grain size increase with the increment of roll speed. The primary grain size decreases firstly and then increases with the increment of the vibration frequency correspondingly. When the casting temperature is from 650℃ to 690℃, the roll speed is 0.069 m·s-1 , and the vibration frequency is about 80 Hz, AZ31 alloy strip with a cross section size of 4 mm×160 mm was prepared by the proposed process. The ultimate tensile strength and elongation are improved 1% and 57%, respectively.     

热型连铸锌铝合金定向凝固线材的组织分析

对热型连铸锌铝合金定向凝固线材的铸态及热处理组织进行了观察、分析和讨论。结果表明：热型连铸锌铝合金线材的显微组织为定向生长的平行柱状枝晶组织;共晶合金ZA5的枝状芥是的每个枝晶都由多层片状共晶β和η两相构成,过共晶合金的组织为初生树枝晶和枝晶间共晶组织,其中ZA8,ZA12初生相为β相,ZA22和ZA27的初生相是α相。     

Zn—Al合金热型连铸定向凝固的晶体生长机理

对热型连铸条件下Zn-Al系列合金引锭时的晶体形核和随后的本的竞争生长过程进行了探讨,组织观察表明,单向热流条件下引锭端部生核的晶粒当其枝晶择优生长方向与热流方向一致时才能生长,其它取向的晶粒逐渐被淘汰,合金的凝固特性对选晶过程有极大的影响,ZA5和ZA8合金由于凝固范围窄,晶体直接由引锭端部的晶粒通过竞争生长获得柱状晶组织,ZA12,ZA22和ZA27含Al量高,凝固范围宽,其平行柱状晶组织是从引锭端部的等轴晶区发展而来的。     

The correlation between dendritic microstructure and mechanical properties of directionally solidified hypoeutectic Al-Ni alloys

Al-Ni hypoeutectic alloys were directionally solidified under upward transient heat flow conditions. The aim of the present study is to set up correlations between the as-cast microstructure and the resulting mechanical properties of these alloys. The dependence of primary and secondary dendrite arm spacing on the alloy solute content and on solidification thermal parameters is also analyzed. The results include transient metal/mold heat transfer coefficient, tip growth rate, cooling rate, dendrite arm spacing, ultimate tensile strength, yield tensile strength and elongation. Expressions relating dendrite spacing to solidification thermal parameters and mechanical properties to the scale of the dendritic microstructure have been determined. It was found that the ultimate tensile strength and the yield tensile strength increase with increasing alloy solute content and with decreasing primary and secondary dendrite arm spacing. In contrast, the elongation was found to be independent of both alloy composition and dendritic arrangement.     

锌铝合金热型连铸的工艺方法

就热型连铸工艺条件下对具有共晶、包晶和共析转变的5种典型锌铝合金的连续定向凝固进行了研究,找出了各种合金的最佳工艺参数配合范围.研究表明引锭操作是热型连铸工艺的关键环节,型口温度、拉铸速度、冷却条件、合金成分和液位压头对铸锭表面质量有直接影响,型口位置的固液区存在着热和力的平衡.只有通过调节工艺参数,维持固液界面的良好位置,才能拉铸出表面光滑的线材.     

热型连铸Cu-Cr合金铸态下的组织与性能

用热型连铸法制备过共晶Cu-Cr合金线．探讨了其在铸态下的微观组织形态、力学性能和导电性能。结果表明：随着含Cr量的增加，Cu-Cr合金的抗拉强度增加，拉铸速度增加，Cu-Cr合金的导电性增加。     

Effects of Cu addition on microstructure and mechanical properties of as-cast Mg-6Zn magnesium alloy

The application of Mg-Zn binary alloys is restricted due to their developed dendritic microstructure and poor mechanical properties. In this study, an alloying method was used to improve the mechanical properties of Mg-Zn alloy. The Mg-6Zn magnesium alloys microalloyed with varying Cu content(0, 0.8, 1.5, 2.0 and 2.5wt.%) were fabricated by permanent mould casting, and the effects of Cu content on the microstructure and mechanical properties of as-cast Mg-6Zn alloys were studied using OM, SEM, XRD and tensile tests at room temperature. The obtained results show that the addition of Cu not only can refine the grains effectively, but also can modify the eutectic morphology and improve the mechanical properties of the alloys. The main phases of the studied alloys include α-Mg, MgZn_2, Mg_2Cu and CuMgZn. When the content of Cu exceeds 0.8wt.%, Mg_2Cu phase appears. Meanwhile, the eutectic morphology is modified into dendritic shape or lamellar structure, which has an adverse effect on the tensile properties. Furthermore, among the investigated alloys, the alloy containing 0.8% Cu shows an optimalultimate tensile strength of 196 MPa, while the alloy with 1.5wt.% Cu obtains an excellent elongation of 7.22%. The experimental alloys under different Cu contents show distinguishing fracture behaviors: the fracture of the alloy with 0.8wt.% Cu reveals a mixed mode of inter-granular and quasi-cleavage, while in other investigated alloys, the fracture behaviors are dominated by cleavage fracture.     

Effect of thermal exposure on microstructure and mechanical properties of Al−Si−Cu−Ni−Mg alloy produced by different casting technologies

The effect of thermal exposure at 350 °C for 200 h on microstructure and mechanical properties was investigated for Al−Si−Cu−Ni−Mg alloy, which was produced by permanent mold casting (PMC) and high pressure die casting (HPDC). The SEM and IPP software were used to characterize the morphology of Si phase in the studied alloys. The results show that the thermal exposure provokes spheroidization and coarsening of eutectic Si particles. The ultimate tensile strength of the HPDC alloy after thermal exposure is higher than that of the PMC alloy at room temperature. However, the TEPMC and TEHPDC alloys have similar tensile strength around 67 MPa at 350 °C. Due to the coarsening of eutectic Si, the TEPMC alloy exhibits better creep resistance than the TEHPDC alloy under studied creep conditions. Therefore, the alloys with small size of eutectic Si are not suitably used at 350 °C.     

Ca对ZA63合金组织和力学性能的影响

通过合金制备、微观分析和力学性能测试等方法研究了Ca对ZA63合金微观组织和力学性能的影响.结果表明,当加入Ca元素后,舍金晶粒细化,半连续网状的τ相变为细小粒状或棒状,颗粒状τ相更为细小,并形成了细小高熔点Al_2Ca相.随着Ca含量的增加,固溶时效态合金在室温、150℃和175℃温度下的抗拉强度和延伸率基本上呈先升高后降低的趋势.当Ca含量为1.0%时,合金在各温度下的抗拉强度和延伸率都达到最大值.     

Effect of mold oscillation on the metallurgical characterization and mechanical properties of A319 aluminum alloy casting

Effect of mold oscillation on metallurgical characterization and mechanical properties of the A319 alloy was investigated. Experimental results show that the microstructure of A319 alloy was significantly refined regarding α-Al grain refinement along with improved silicon particle morphology due to mold oscillations. Mechanical properties of casting such as tensile strength, yield strength, percentage elongation and micro-hardness improved by 39.05, 28.05%, 2.67 times and 27.02% respectively as compared to that of stationary casting. This investigation is an attempt to study the effect of mold frequency on mechanical and metallurgical properties of aluminum alloys.