Microstructures and fatigue behavior of metal-inert-gas-welded joints for extruded Al-Mg-Si alloy

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Vol. 745; pp. 63 - 73
• Main Authors: Lin, Sen, Deng, Yun-Lai, Tang, Jian-Guo, Deng, Shu-Hao, Lin, Hua-Qiang, Ye, Ling-Ying, Zhang, Xin-Ming
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 04.02.2019; Elsevier BV
• Subjects: Al-Mg-Si alloy; Aluminum base alloys; Crack propagation; Crystal defects; Extrusion; Fatigue behavior; Fatigue failure; Fatigue tests; Fracture mechanics; Gas metal arc welding; Heat affected zone; Heat treating; Magnesium; Mechanical properties; Metal fatigue; Microstructures; MIG-welded joint; Silicon; Stress concentration; Tensile tests; Ultimate tensile strength; Weld defects; Welded joints; Welding defects; Al-Mg-Si alloy; Welding defects; Fatigue behavior; Microstructures; MIG-welded joint
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2018.12.080

An extruded profile of Al-Mg-Si alloy was metal-inert-gas-welded (MIG-welded) with an ER5356 filler wire and the microstructures, mechanical properties and fatigue behavior of the joints were investigated. Compared with the base material (BM), coarser grains are present in the heat-affected zone (HAZ) as a result of abnormal growth in the welding process. The average grain sizes of the weld zone (WZ) and BM were 40.8 µm and 16.8 µm, respectively. The ultimate tensile strength (UTS) of the MIG-welded joint and BM were 210.3 MPa and 274.8 MPa, respectively, thus, the weld joint efficiency was approximately 76.5%. Fracture appeared at the location with the minimum hardness in the HAZ of the MIG-welded joint during tensile tests. Based on the fatigue testing experiment with 107 cycles, the conditional fatigue strengths of the MIG-welded joint and BM were 61.7 MPa and 141.3 MPa, respectively. Welding defects, such as coarse secondary phase, welding pores and incomplete fusion, caused local stress concentration which initiated fatigue crack and apparently increased the fatigue crack growth rate of the MIG-welded joint, ultimately causing the premature fracture of the joint at the WZ.