热旋锻对AZ61镁合金显微组织与力学性能的影响

Microstructure and mechanical properties of AZ61 Alloy Processed by Rotary Swaging

摘要:

通过多道次热旋锻，成功制备了AZ61镁合金丝棒材，经细晶强化及纳米级颗粒强化显著提高了AZ61合金强度，并讨论了动态沉淀析出机理。结果表明：旋锻AZ61镁合金平均晶粒直径约为8μm，YS为302MPa，UTS达376MPa，具有中等延伸率（7%）。纳米级沉淀相在旋锻变形过程中动态析出，这些沉淀相包括：晶内析出直径50-140nm的球形β-Mg17Al12相（~6.5vol.%）、平均直径10nm的球形Al6Mn相。大量细小纳米级第二相动态析出的机理为：旋锻是塑性变形-静态时效-塑性变形-静态时效交替进行的高频（锻打频率通常在1500－6000次/分）脉冲式热力加工过程。塑性变形产生的位错、空位等缺陷，为第二相析出提供了大量优先形核位置。并且每一脉冲周期中静态时效的时间很短（约为0.05s数量级），所以析出的第二相不会长的过大。

Abstract:

The AZ61 magnesium alloy wires and sticks were prepared through multi-step hot rotary swaging, and the strength of AZ61 alloy is enhanced due to grain refinement and dynamic precipitation during rotary swaging process. The dynamic precipitation mechanism during hot rotary swaging is also discussed. The results show that the rotary swaged AZ61 alloys exhibited a high YS of 302MPa, a high UTS of 376MPa and a elongation of 7%. The means grain sizes in rotary swaged AZ61 alloy is 8μm. The dynamicly precipitated nanophases during rotary swaging process of AZ61 alloy include spherical Mg₁₇Al₁₂ particles (average size of 110nm, ~6.5 vol.%) and spherical Al₆Mn particles (average size of 10nm). The dynamic precipitation mechanism during rotary swaging process is as follows: rotary swaging is a high-frequency pulse forging process (the pulse forging frequency is between 1500 and 6000 strokes per minute) during which plastic deformation intervals altered with aging intervals. These crystal defects produced during plastic deformation such as dislocations and vacancies provided large amount of nucleation sites for precipitation. The aging interval during each pulse period is as short as 0.05s and hence the dynamic precipitate phases didn’t grow to a very large size.