油气润滑对AZ80镁合金铸坯表面质量和组织的影响

Effect of oil-gas slip on surface quality and solidification structure of AZ80 magnesium alloy billets

本文以自主设计的镁合金油气润滑铸造装置制备了直径154mm的AZ80镁合金铸坯,系统研究油气润滑对AZ80镁合金铸坯表面质量和凝固组织的影响,并对其机理进行了探讨。采用结果表明:采用油气润滑铸造时,氩气和润滑油在石墨环内表面形成了一层油气混合膜,改变了熔体和结晶器的接触方式和热交换状态,从而制备出高品质的AZ80镁合金铸坯。随着气体压力的增加,铸坯表面粗大的偏析瘤和皮下偏析层得到抑制,凝固组织得到了明显细化。当气体压力增加到0.4 MPa时,铸坯皮下偏析层厚度从1252μm降至628μm,铸坯R/2、心部晶粒尺寸和二次枝晶间距显著减小。随着凝固组织的细化,Al、Zn和Mn元素的宏观偏析得到了改善。

AZ80magnesium alloy billets with diameter of 154 mm were prepared using oil-gas slip casting device designed in dependently.The effects of oil-gas slip on surface quality and solidification structure of AZ80 magnesium alloy billets were systematically studied and theoretically discussed.The results indicate that high quality AZ80magnesium alloy billets can be prepared by oil-gas casting process.Argon and lubricating oil form an oil-gas film on the inner surface of the graphite ring,which changes the contact mode and thermo exchanging state between melt and graphite ring.With the increase of gas pressure,the coarse segregation tumors and the subsurface segregation layer on the billets surface are inhibited,and the solidification structure is refined obviously.When the gas pressure increases to0.4 MPa,the thickness of subsurface segregation layer decreases from 1252μm to 628μm,and the grain size and secondary dendrite spacing at R/2 and center of the billets decrease significantly.Meanwhile,macrosegregation of Al,Zn and Mn elements is improved with the refinement of solidification structures.