Zn-8%Al变形锌合金组织演化规律研究

Microstructure Modification of Wrought Zn-8%AlZn-based Alloy

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。

Zn-8%Al alloy was manufactured through casting, extrusion and drawing technique. The microstrueture and phase transition were observed under OM and SEM. The peritectic （ L-→α＋β） , euteetic （ L→η＋β） and eutectoid （ β→η＋α） mierostructures 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 recrystal- lization. The continuous transformation η→η′m＋η′→η＋α may take place besides dynamic recrystallization and recovery in the drawing process.