氩气处理对AZ91含气量及组织的影响

Effect of Argon Degassing on Hydrogen Content and Microstructure of AZ91 Magnesium Alloy

AZ系镁合金中的高含气量(含氢量)往往导致铸造组织疏松问题。本试验研究了AZ91镁合金氩气除气工艺,主要研究了氩气流量、处理时间及处理方式对AZ91镁合金含气量及组织的影响。结果表明,常规熔铸AZ91镁合金含气量在9.2~10.3μg/g左右,经氩气处理后,合金含气量可最低降至5.2μg/g。氩气除气率与氩气流量及处理时间密切相关,增大氩气流量和延长处理时间,除气率提高。分步除气处理的效率高于连续处理,同时氩气处理后铸造组织也有明显细化效果,这可能与氩气的搅拌作用促进熔体中异质形核心均匀分布促进形核率提高有关。当氩气流量为1.0 L/min,两步处理的时间分别为2和1 min时,除气率可达43.7%,铸造组织平均晶粒尺寸由未处理的300μm降低至230μm。

The porosities of AZ series magnesium alloys usually occur due to the high gas （hydrogen） concentration. Argon degassing process of AZ91 magnesium alloy is investigated in this paper, as well as the effects of argon flow rate, treating time and treating schedule on the hydrogen content and microstructures of the AZ91 alloy. The results show that the average hydrogen content of AZ91 by traditional casting technology was around 9.2-10.3μg/g. After argon degassing, the hydrogen content can be reduced to 5.2μg/g. The degassing efficiency is much related to the argon flow rate and treating time. Increasing the flow rate and prolonging treating time can promote the degassing efficiency. Meanwhile, a multiple step treatment have stronger degassing efficiency than a continuous one, and the refinement effect of rnicrostructures is found after argon degassing process, which maybe due to the homogenization of heterogeneous nuclei by the forced convection of argon gas. The degassing efficiency can reach 43.7% when taking a dual step process （2 min and 1 min） at the flow and treating time of 1.0 L/min and 3 min respectively. The average grain size decreases from 300μm to 230 p,m after the process.