Fabrication and microstructure evolution of semi-solid LY11 alloy by SIMA

For semi-solid metal forming, it is essential to fabricate the semi-solid materials with spheroidal microstructure. Among several fabrication techniques of the semi-solid materials, (strain-induced melt activation (SIMA) is an ideal candidate with the advantages of simplicity and low equipment costs. In this paper, the microstructure evolution of LY11 alloy (approximately corresponding to ASTM 2017) was investigated in the SIMA process, which had two essential stages: deformation and isothermal heat treatment. The deformation stage was conducted using a CSS-1100C material testing machine and the isothermal heat treatment stage was performed in a resistance furnace. Different levels of deformation temperatures, ram velocities, isothermal temperatures, and holding times were used in this investigation. The microstructure of LY11 alloy was observed by a NEOPHOT-1 optical microscope. The results indicated that the processing parameters must be selected properly to obtain the fine, uniform and spheroidal microstructure by SIMA. The deformation-recrystallization mechanism for microstructure evolution in SIMA process was supported by experimental evidence.     

SIMA法制备7A04合金半固态触变组织的演化

研究了二次加热工艺参数对SIMA法制备7A04合金半固态触变组织的演化规律.结果表明:随着加热温度的升高和保温时间的延长,晶粒的形状逐渐趋于球形.当加热温度低于610℃时,晶粒尺寸不断长大,而后逐渐减小.在保温的初始阶段,共晶液相没有完全浸润晶粒边界,晶粒的聚结长大处于主导地位.当保温时间达到4min左右时,共晶液相几乎充满了所有的晶界,Ostwald长大扩散机理处于主导地位.晶粒长大规律符合动力学方程.     

Structure evolution of AZ61 magnesium alloy in SIMA process

The effect of prior compressive deformation, isothermal temperature and holding time on the structure of AZ61 magnesium alloy fabricated by strain-induced melt activation(SIMA) processing was investigated. The specimens were subjected under deformation ratios of 0%, 22% and 40% and various heat treatment time and temperature regions. The results indicate that the ideal technological parameters of semi-solid AZ61 alloy produced with non-dendrites are recommended as 22% (prior compressive deformation), 595℃ (heat treatment temperature) and 40 min(time). The as-cast AZ61 magnesium alloy isn‘t fit for semi-solid forming.     

Effect of RE elements on the microstructural evolution of as cast and SIMA processed Mg-4Al alloy

In the present article, the effect of Rare Earth elements on the microstructural development of as cast and semisolid Mg-4Al alloy produced by SIMA process is studied. Investigation conducted by metallographic observation, scanning electron microscope and quantitative metallographic methods. Results showed that alloy's dendrites turn into larger fully dendritic shape with sharp and narrow arms from equiaxed rosette type as the amount of RE elements increased from 0 through 4%. The effect of RE elements on the microstructure of the treated-alloys was detectable through elimination of vast number of intragranular liquid droplets as well as by decreasing kinetic of microstructural changes. It was shown that the trend of grain coarsening decreased drastically by addition of RE elements to the Mg-4Al alloy during partial remelting at 610 °C. Moreover, the effect of REs on the other parameters such as fraction of liquid, shape factor and particle size was studied.     

Mechanical behavior of LC_4 alloy in semisolid state at high volume fractions of solid

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SIMA制备半固态LY11合金的工艺研究

研究了应变诱发熔化激活法 (SIMA)制备半固态LY11合金过程中的变形温度、变形速度、等温温度和保温时间等工艺参数对LY11合金组织演变的影响。研究结果表明 ,要获得均匀、细小的非枝晶组织 ,必须合理地匹配SIMA工艺参数     

AZ91镁合金的SIMA法半固态组织特征

研究了挤压态AZ91镁合金的SIMA法半固态组织演变.结果表明:挤压合金为以α-Mg再结晶等轴晶为主相,与极少量细粒状成串分布于α-Mg基体上的Mg17Al12颗粒组成的两相组织,基体中存在大量的大角度亚晶及高密度的位错缠结.在二次加热过程中,原子扩散通道多,晶界液化及颗粒球化所需的加热温度低,等温时间短.565℃等温5min,即可获得固相率为57%,颗粒平均直径为58 μm、形状圆整、分布均匀的半固态组织.等温5 min后,半固态颗粒发生长大,其长大机制为Ostwald熟化.     

Study on the effects of the compression ratio and mushy zone heating on the thixotropic microstructure of AA 7075 aluminum alloy via SIMA process

The effects of compression ratios on the microstructure evolution of semisolid Al7075 alloy produced by the strain induced melt activation (SIMA) process were investigated. The samples were cold deformed by compression into the different heights up to 40% reduction. The isothermal holding treatments within mushy zone of the alloy were carried out at 610, 620 and 625 °C for predetermined time intervals.The results revealed that the average grain size gradually reduced with the increase in the compressive ratio. While the compressive ratio surpassed 30%, the descending trend above was not as evident as that of below 30% reduction. The optimum condition presenting the minimum grain size and the maximum shape factor with the highest uniformity is discussed. During the subsequent mushy zone heating, the recrystallization was induced in the deformed samples by the increasingly accumulated strain energy.     

SIMA法制备LC4半固态合金的流变行为研究

半固态坯的流动性能是获得优质、复杂制件的基础和关键。通过对两种状态合金在相同载荷作用下进行半固态压缩试验,结果表明:挤压态合金的流动性最差,挤压后冷变形态合金Ⅱ(压缩方向垂直于冷变形方向)的流动性最好。这主要有两方面的原因:一是晶粒形状上的差异;二是与半固态坯料的制备历史及其后续加工有关。     

SIMA法制备LC4半固态合金的流变行为研究

半固态坯的流动性能是获得优质、复杂制件的基础和关键。通过对两种状态合金在相同载荷作用下进行半固态压缩试验，结果表明：挤压态合金的流动性最差，挤压后冷变形态合金Ⅱ（压缩方向垂直于冷变形方向）的流动性最好。这主要有两方面的原因：一是晶粒形状上的差异；二是与半固态坯料的制备历史及其后续加工有关。