热处理对汽车用AZ91镁合金微观组织和力学性能的影响

Effect of Heat Treatment on Microstructure and Mechanical Properties of AZ91 Magnesium Alloy for Automobile

研究了汽车用AZ91镁合金挤压后固溶时效处理对其微观组织和力学性能的影响。结果表明：AZ91镁合金的微观组织主要由基体α-Mg和约20.6wt%的β-Mg17Al12相组成,晶粒平均尺寸约为22μm。固溶处理后合金发生再结晶,β相完全回溶到α-Mg基体,约有15.6wt%的二次β相在时效过程中析出。AZ91镁合金在410℃固溶8 h后拉伸强度略微增大,而固溶处理16 h后拉伸强度降低。合金随后在200℃时效8～16 h的过程中析出细小二次β相,增加了晶内位错运动和晶界滑动阻力,使合金的拉伸强度逐渐增大。时效24 h后因细小二次β相的粗化而使合金力学性能降低。挤压态AZ91镁合金较优的固溶时效工艺为：410℃×8 h,空冷＋200℃×16 h,空冷。

The effects of solution and aging treatment on microstructure and mechanical properties of extruded AZ91magnesium alloy for automobile were studied. The results show that the microstructure of AZ91 magnesium alloy is mainlyconsisted oftx-Mg matrix and about 20.6wt% 13-Mg,7AII2 phase, and the grain average size of the alloy is about 22 μm. Aftersolid solution treatment, the rccrystallization of the alloy occurs, 13 phase completely dissolves into et-Mg matrix, and thesecond 13 phase about 15.6wt% is precipitated during the aging. The tensile strength of the AZ91 magnesium alloy improvesslightly after solid solution at 410 ℃ for 8 h, and it decreases after solid solution at 410 ℃ for 16 h. As the alloy precipitatesfine second 13 phases in the subsequent aging process at 200 ℃ for 8-16 h, which increases dislocation motion and grainboundary sliding resistance, and the tensile strength of the alloy increases gradually. The mechanical properties of the alloydecrease after aging for 24 h due to the coarsening 13 phase. The optimal solution and aging process of extruded AZglmagnesium alloy is 410 ℃x8 h, air cooling ＋ 200 ℃xl6 h, air cooling.