Mg-6Zn-1Cu-0.3Mn镁合金的半固态组织演变

Semi-solid Microstructure Evolution of Mg-6Zn-1Cu-0.3Mn Magnesium Alloy

采用半固态等温热处理法,研究了重熔温度和等温时间对Mg-6Zn-1Cu-0.3Mn镁合金半固态组织演变的影响。结果表明:在不同温度保温30min或在585℃保温不同时间的球化演变过程中,Mg-6Zn-1Cu-0.3Mn合金中球状组织的平均尺寸、形状因子均先减小后增大,且固相率明显下降;晶界和亚晶界共同提供了溶质原子的扩散通道和液相相互渗透的路径,晶粒内部的溶质原子Zn、Cu和Mn富集区和枝晶壁搭接处形成了高溶质浓度的小"液池";当保温温度超过585℃或时间超过30 min时,颗粒易于粗化,其粗化符合Ostwald熟化机制。适合Mg-6Zn-1Cu-0.3Mn合金的半固态等温处理工艺为585℃×30 min,其颗粒平均尺寸、形状因子和固相率分别为29.91μm、1.09和47.55%。

The effects of remelting temperature and holding time for the semi-solid microstructure evolution of Mg-6Zn-1Cu-0.3Mn magnesium alloy were studied by semi-solid isothermal heat treatment.The results show that with holding temperature and time prolonging,the acceleration of the remelting process and change in the microstructure is acquired,in the process of spherical evolution at different temperatures for 30 min or at 585℃for different time.The average size and shape factor of the spherical semi-solid microstructure first decrease and then increase,while the solid fraction decreases sharply.The grain boundaries and sub-boundaries both provide the solute atoms with diffusion aisles and the liquid phase with interpenetration path,and the“liquid pools”of high solute concentration form at the rich Zn,Cu and Mn solute atoms regions and the dendrite arms overlap.With the holding temperature exceeding 585℃or the heat preservation time over 30 min,the primary particles tend to merge and grow up,consistent with the rule of Ostwald ripening mechanism.The fitting heat treatment parameters is reheating for 30 min at 585℃for semi-solid isothermal heat treatment of the alloy,and the average particle size,shape factor and solid fraction of the alloy are 29.91μm,1.09 and 47.55%,respectively.