热处理对AZ31B镁合金搅拌摩擦焊焊接接头显微组织和显微硬度的影响

Effect of Heat Treatment on Microstructure and Microhardness of Friction Stir-welded Joints for AZ31B Magnesium Alloy

对AZ31B镁合金进行搅拌摩擦焊接及焊后热处理,研究了热处理前后焊接接头显微组织及显微硬度的变化规律。结果表明:随着退火温度的升高,AZ31B镁合金搅拌摩擦焊接接头前进侧和后退侧的分界线逐渐消失;在热处理过程中,由于焊核区所吸收的能量主要用于晶粒的长大,而热影响区和热机影响区结合区域在再结晶时消耗了较多的能量,导致了焊核区晶粒的长大速率大于热影响区和热机影响区结合区域的;当退火温度低于200℃时,热机影响区的显微硬度高于焊核区,并且前进侧热机影响区的显微硬度略高于后退侧的;当退火温度高于250℃后,热机影响区的显微硬度显著下降;随着退火温度的升高,热影响区的显微硬度略有下降。

Friction stir welding and postweld heat treatment were conducted on AZ31B magnesium alloy. The variation rule of mierostructure and microhardness of welding joints before and after heat treatment was studied. The results show that as the annealing temperature increase, boundaries at both the advancing side and the retreating side of the welding joint disappeared gradually. During the process of heat treatment, energy obtained by welding nugget zone （WNZ） was mainly responsible for the grain growth, but more energy had been consumed during recrystallization in dilution zone of heat affected zone （HAZ） and thermo-mechanically affected zone （TMAZ）, which caused the grain growing speed in WNZ was higher than that of in the dilution zone. When the annealing temperature was under 200℃, the microhardness of TMAZ was higher than that of WNZ. Moreover, the mircohardness at the advancing side of TMAZ was slightly higher than that of at the retreating side. When the annealing temperature was above 250℃, the microhardness of decreased distinctively. As the annealing temperature increase, the microhardness of HAZ decreased slightly.