Effect of isothermal heat treatment on microstructure of Mg-7Zn-0.3Li-xNd alloy
The isothermal heat treatment(SSIT)was used to treat Mg-7Zn-0.3Li-xNd alloys with different Nd contents(x=0.1,0.3,0.5,0.7)at different temperatures and holding time.The influences of holding temperature and holding time on the evolution of non-dendrite microstructure in Mg-7Zn-0.3Li-xNd alloys were studied,and the formation mechanism of non-dendrite particles was analyzed.The results show that Mg-7Zn-0.3Li-0.5Nd alloy obtains ideal spherical non-dendrite particles held at 580℃for 30 min,with solid phase ratio,average grain size,and shape factor of 71.9%,47 μm and 1.85,respectively.With the increase of holding temperature or the extension of holding time,the average grain size and shape factor of non-dendrite particles reveal a trend of first decreasing and then increasing,while the solid content continues to decrease.With the changes of temperature and time,the evolution process of non-dendrite structure can be mainly divided into three parts,namely dendrite coarsening,separation and spheroidization,and merging and maturation.
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