通过预涂覆SiC优化AZ31B镁合金DE-GMAW焊缝的显微组织及提升力学性能

研究了碳化硅(SiC)颗粒涂覆量对2mm厚AZ31B镁合金双电极气体保护焊DE-GMAW焊缝的宏观形貌、显微组织和力学性能的影响。利用光学显微镜、扫描电镜和X射线衍射分析技术(XRD)对接头的显微组织、相及相的成分进行分析。同时采用维氏硬度试验计和万能试验机对焊接接头的显微硬度和抗拉强度分别进行测量。结果表明,随着SiC涂覆量的增加,焊接接头熔深和深宽比先增大后减小。XRD测试结果显示,SiC的添加并不改变焊缝中相的组成,焊缝由α-Mg和β-Mg_(17)Al_(12)组成。SiC可以细化α-Mg晶粒,打断焊缝中β-Mg_(17)Al_(12)相,起到弥散强化的效果。但SiC涂覆量达到一定值后,随着SiC涂覆量的继续增加,α-Mg晶粒粗化,β-Mg_(17)Al_(12)相的弥散强化作用不再增加。焊接接头的显微硬度和抗拉强度随着SiC涂覆量的增加先增大后减小。

Improved Microstructure and Promoted Mechanical Properties of DE-GMAW Weld Seam of AZ31B Magnesium Alloy by Pre-coating SiC

The effects of SiC coating on weld seam's macro-morphology,microstructure and mechanical properties of doubleelectrode gas metal arc welded (DE-GMAW) 2 mm thick AZ31B magnesium alloy were investigated.The microstructure,phase and phase composition of the weld seams were observed by optical and scanning microscope,X-ray diffraction,micro hardness test and tensile tests.The results showed that the penetration and the depth/width (D/W) ratio of the weld seam increased at first and then decreased with the increasing amount of the SiC coating.The results of the XRD analysis showed that the addition of SiC could not change the types of phases in the weld seam,it contained a-Mg and β-Mg17Al12.The effects of SiC were refining grain sizes and interrupting the β-Mg17Al12 phase in the weld seam,this interruption had dispersion strengthening effect.But when the amount of SiC reached a certain value,the α-Mg grains coarsened with the increasing SiC amount and the dispersion strengthening effect of the β-Mg17Al12 phase would no longer increase.The microhardness and ultimate tensile strength of the seams increased at first and then decreased with the increasing amount of coated SiC.