Fatigue strength and fatigue crack initiation mechanism in non-combustible Mg-4%Al-1%Ca-0.2%Mn alloys and its TIG and MIG weld joints

IF 2.4 4区材料科学 Q2 METALLURGY & METALLURGICAL ENGINEERING

Welding in the World Pub Date : 2024-07-28 DOI:10.1007/s40194-024-01813-6

Xuanyi Shao, Bui Phuong Thao, Taiki Nakata, Nan Zhang, Yukio Miyashita, Shigeharu Kamado

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Abstract

The fatigue mechanism of a Mg-4%Al-1%Ca (hereinafter referred to as AX41) non-combustible magnesium alloy and its TIG (tungsten inert gas) and MIG (metal inert gas) weld joint was investigated through the plane bending fatigue and crack propagation tests. Results of plane bending fatigue tests showed that fatigue strengths of TIG and MIG weld joints were lower than that of the base metal (BM), while a similar fatigue strength at 10⁷ cycles was found in both TIG and MIG weld joints. However, a TIG weld joint showed the highest crack propagation resistance among tested samples in crack propagation tests. Scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) analysis were used to investigate the relationship between microstructural factors and the crack initiation mechanism of AX41 alloy and its weld joint. Cracks were found to initiate from grains in BM, while weld defects became a crack initiation site in a MIG weld joint. However, both grains and weld defects were observed as a crack initiation site in a TIG weld joint. Results of EBSD analysis indicated that fatigue crack initiation in TIG weld joint was favored in large grains with high Schmid factors. The critical value of initial crack length was discussed in the correlation between the maximum grain size and the maximum weld defects/inclusions size on the fatigue crack initiation mechanisms. As a result, a prediction method of the fatigue strength at 10⁷ cycles was proposed based on the hardness and weld defects/inclusions size.

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不可燃 Mg-4%Al-1%Ca-0.2%Mn 合金及其 TIG 和 MIG 焊点的疲劳强度和疲劳裂纹起始机制

通过平面弯曲疲劳和裂纹扩展试验，研究了Mg-4%Al-1%Ca（以下简称AX41）不燃镁合金及其TIG（钨惰性气体）和MIG（金属惰性气体）焊接接头的疲劳机理。平面弯曲疲劳试验结果表明，TIG和MIG焊接接头的疲劳强度低于母材（BM），而TIG和MIG焊接接头在107次循环时的疲劳强度相似。在裂纹扩展试验中，TIG焊接接头的抗裂纹扩展性能最高。采用扫描电镜（SEM）和电子背散射衍射（EBSD）分析了AX41合金及其焊缝裂纹萌生机制与显微组织因素的关系。发现裂纹是由BM中的晶粒引发的，而焊缝缺陷成为MIG焊接接头裂纹的起爆点。然而，在TIG焊接接头中，晶粒和焊缝缺陷都是裂纹起裂部位。EBSD分析结果表明，大晶粒、高施密德因子有利于TIG焊接接头疲劳裂纹的萌生。从最大晶粒尺寸与最大焊缝缺陷/夹杂物尺寸之间的关系出发，讨论了初始裂纹长度临界值对疲劳裂纹萌生机制的影响。提出了一种基于硬度和焊缝缺陷/夹杂物尺寸的107次循环疲劳强度预测方法。

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来源期刊

Welding in the World METALLURGY & METALLURGICAL ENGINEERING-

CiteScore

4.20

自引率

14.30%

发文量

181

审稿时长

6-12 weeks

期刊介绍： The journal Welding in the World publishes authoritative papers on every aspect of materials joining, including welding, brazing, soldering, cutting, thermal spraying and allied joining and fabrication techniques.