浇注温度对AZ31镁合金连续流变挤压成形组织的影响

研究了不同浇注温度、辊靴型腔中不同位置的AZ31镁合金组织.结果表明,浇注温度高于750℃时,半固态区减小,工作辊对半固态区枝晶的剪切时间变短,枝晶破碎不充分,得不到优质的半固态金属浆料;浇注温度低于730℃时,固相区变大,半固态区部分枝晶未得到充分剪切就进入了固相区,固相区的枝晶更是难以断裂,因此得不到理想的半固态组织;随着固相区的增加,合金变形更加困难,设备工作压力增加,使用寿命降低;AZ31镁合金连续流变挤压最佳浇注温度为730～750℃.

Effect of Casting Temperature on Microstructure of AZ31 Alloy in Continuous Rheo-Extrusion Process

Casting temperature is the main influencing factor on microstructure in the continuous rheo-extrusion process of AZ31 magnesium alloy. The microstructures of AZ31 magnesium alloy at different positions in the roll-shoe die cavity during continuous rheo-extrusion were investigated at different casting temperatures. The results showed that the semi-solid zone becomes smaller when the casting temperature is higher than 750 ℃, and the time the work roll takes to prune the dendrite in the semi-solid zone is shortened, i.e., the dendrite has not been fully broken up, thus making the high-quality semi-solid alloy unavailable. On the other hand, when the casting temperature is lower than 730 ℃, the solid-state zone becomes bigger and the semi-solid zone where part of the dendrite has not been fully pruned is merged into the solid-state zone, thus making the dentrite in solid-state zone more difficult to be broken up. As a result, it's impossible to get an ideal semi-solid microstructure. With the solidification zone thus increased, the alloy is deformed more difficultly with increasing working pressure needed for the equipment system and its service life shortened. The best casting temperature is 730～750 ℃ in the continuous rheo-extrusion process of AZ31 alloy.