采用应变诱导熔化激活法(SIMA法)制备了半固态7050 铝合金坯料, 研究了等温过程中晶粒的粗化规律.利用Gleeble—3500热模拟试验机分别对半固态7050铝合金和常规铸造7050铝合金进行了压缩实验,分析了其应力—应变关系, 研究了半固态7050铝合金压缩变形时液固相协同变化规律,并对半固态7050铝合金和常规铸造7050铝合金的压缩裂纹扩展过程进行了研究.结果表明, 常规铸造的7050铝合金的压缩应力明显偏高.变形量、变形温度和应变速率对显微组织变化和液相分布有明显影响. 此外,由于半固态合金和铸造合金在显微组织上的显著差别,导致其裂纹的扩展过程也不一样, 即分别对应着固—液分离过程和固—液、固—固混合分离过程.

The compression characters of the semi—solid slurries are the key to semi—solid processing such as semi—solid rolling which has high strain rates during the deformation. The deformation mechanism of semi—solid alloy can be understood well only after the relationship between stress and strain is obtained. Among many relevant research works done up to now, very few studies focus on the 7050 aluminum alloy. In order to study the sensibility of 7050 aluminum alloy to the strain rates, temperatures and reductions, the deformation behavior and microstructure evolution of 7050 aluminum alloy under different compression parameters were studied in this work. The grain coarsening of 7050 aluminum alloy prepared by the strain induced melt activation (SIMA) method during the isothermal heating process was studied firstly. Then the compression tests, within the semi—solid temperature range, on conventional cast alloy and semi—solid alloy were carried out respectively by using a Gleeble—3500 material thermo—simulation machine with the strain rates from 0.1 s^-1 to 10 s^-1.The relationship between stress and strain was analyzed subsequently. The synergistic effect between liquid and solid was analyzed in—depth as well. In addition, the differences of cracks propagation between conventional cast alloy and semi—solid state alloy during compression were discussed. Experimental results show that the stress of conventional cast alloy has a higher level than that of semi—solid alloy, which is 12 MPa higher at the peak position and 9 MPa higher during the stabilization stage. Reductions, deformation temperatures and strain rates during compression have remarkable effects on the microstructure evolution and the liquid phase distribution. The high reduction leads to the sharp deformation of the grain shape. The deformation has an obvious transition region in the middle which can be clearly seen that elongated grains have a deflection toward the edge. The lower the temperature, the smaller the liquid fraction is. This leads to recrystallization during the compression. The strain rates contribute to the flowing and distribution of liquid phase. The liquid phase transfers hardly when consisting with the solid phase under the high strain rate (10 s^-1), which results in a uniform deformation in different regions. Because of the remarkable differences in microstructures between conventional cast alloy and semi—solid alloy, the evolution of cracks propagation is also different, which corresponds to a solid—liquid separation mechanism and a mixed separation mechanism respectively. Semi—solid alloy has spherical crystals that can slide easily when comparing with conventional cast alloy with dendritic crystals. This makes a further explanation for the lower stress of the semi—solid alloy.