摘要:
通过对Zn-8%Al合金的熔铸、挤压和拉拔加工, 采用金相显微镜、扫描电镜等分析手段, 研究了该合金的组织演化和相转变规律。实验结果表明, 铸锭凝固初期发生包晶反应L+α→β, 初生晶α'边缘包围着一层更富Zn的η相, 随着温度的不断下降, 进而发生共晶反应L→η+β与共析反应β→η+α。在热挤压过程中, 大变形量加工使得枝晶破碎, 合金的微观组织得到明显细化, 但在横截面上仍可以看到小的枝晶, 包晶相β在挤压的过程中已经发生共析转变:β→α+η。由于挤压和拉拔过程中都产生大量的变形热, Zn为层错能高的金属, 发生动态再结晶, 但由于冷却速度很快, 只能发生不完全动态再结晶。Zn在冷加工过程中, 出现软化现象, 除了可能发生动态回复与动态再结晶外, 还有可能会发生η→ηm'+η'→η+α的相变。
Abstract:
Zn-8%Al alloy was manufactured through casting, extrusion and drawing technique.The microstructure and phase transition were observed under OM and SEM.The peritectic (L+α→β), eutectic (L→η+β) and eutectoid (β→η+α) microstructures were dominative in solidification of casting, then coarse-grained dentrite was broken and fined during extrusion process, meanwhile the eutectoid transition β→ α+η took place.The dynamic recrystallization was considered due to high distortion heat during extrusion and drawing processes.The work softening was explained in term of dynamic recovery and recrystallization.The continuous transformation η→ηm'+η'→η+α may take place besides dynamic recrystallization and recovery in the drawing process.
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