退火工艺对AZ31镁合金熔焊接头残余应力及微观组织的影响

Influence of Annealing Process on Residual Stress and Microstructure of Welded Joints of AZ31 Alloy

采用不同去应力退火工艺（T=250、350、400℃,t=1-4 h）对AZ31镁合金焊接接头进行真空热压去应力退火处理,采用盲孔法研究镁合金焊接接头退火前后的残余应力变化规律,利用金相显微镜观察接头显微组织。结果表明：经真空热压去应力退火后,镁合金焊接接头残余应力消除效果显著,且退火温度越高,残余应力越低,应力松弛效果越好,350℃时,接头应力松弛率达到85%以上;保温时间对接头残余应力的松弛影响并不显著;随着退火温度的升高,接头显微组织呈现规律性变化,当温度在350℃以上时,晶粒显著长大,且β-Mg17Al12相显著增加;保温时间越长,晶粒平均尺寸越大;最后得到AZ31镁合金焊接接头的真空热压去应力退火最佳工艺为350℃×1 h。

The different temperature and time parameters（T=250℃, 350℃, 400℃, t=1~4h） were adopted in the vacuum hot-compression stress relieving annealing processes of welded joints of AZ31 alloy. The evolution of residual stress was researched by Blind-Hole method and the microstructure of the welded zone was also observed by optical metallographic microstructure. The results show that the removing effect of residual stress is remarkable after vacuum hot-compression stress relieving annealing. The higher the annealing temperature is, the lower the residual stress is, and the better the stress relaxation is. At 350℃, the rate of stress relaxation is 85%. The effect of holding time on the welding residual stress relaxation of magnesium alloy is not significant. The microstructure of the welded joint changes regularly with the increasing temperature.When the temperature is above 350 ℃, the grain significantly grows up and β-Mg17Al12 phase increases significantly. The longer the holding time, the greater the average grain size. Finally, the vacuum hot-compression stress relieving annealing schedule of AZ31 alloy welded joints at 350℃ for 1h can be obtained.