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<p>Three types of resistance spot welds (RSWs), namely, AA5754 to AA5754, to low carbon steel (LCS), and to high-strength low-alloy (HSLA) steel, were successfully welded using multi-ring domed (MRD) electrodes and multistage solidification weld schedules. More FeAl<sub>3</sub> was found by transmission electron microscopy (TEM) in the aluminum weld nugget of AA5754-HSLA RSWs, leading to a higher microhardness and shear strength of the aluminum weld nugget in AA5754-HSLA stack-ups. Martensite was observed in the HSLA sheet, while ferrite and austenite were found in the LCS sheet after welding. The microhardness of the HSLA steel weld nugget increased significantly (~300&#xa0;Hv) compared with base material, due to the formation of martensite. However, the slight increase (~18&#xa0;Hv) in the LCS steel weld nugget was attributed to the formation of austenite, as the temperature in LCS weld nugget was higher than Ac<sub>1</sub> while lower than Ac<sub>3</sub>, austenitizing temperature. Thermal analysis using the SORPAS software revealed that a higher temperature occurred in the HSLA steel compared that in the LCS during resistance spot welding, driving a greater dissolution of Fe into the molten AA5754, leading to the higher microhardness and shear strength of weld nugget in aluminum alloy of the AA5754-HSLA RSWs.</p>

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Strengthening Mechanism of Aluminum Weld Nugget in Novel Dissimilar Resistance Spot Welds of AA5754 to Steels

  • 期刊论文

  • 发表日期：

    2025年3月5日

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  • Liting Shi,
  • Blair E. Carlson,
  • Siwei Li,
  • Hassan Ghassemi-Armaki,
  • Guanyou Li

摘要

Three types of resistance spot welds (RSWs), namely, AA5754 to AA5754, to low carbon steel (LCS), and to high-strength low-alloy (HSLA) steel, were successfully welded using multi-ring domed (MRD) electrodes and multistage solidification weld schedules. More FeAl3 was found by transmission electron microscopy (TEM) in the aluminum weld nugget of AA5754-HSLA RSWs, leading to a higher microhardness and shear strength of the aluminum weld nugget in AA5754-HSLA stack-ups. Martensite was observed in the HSLA sheet, while ferrite and austenite were found in the LCS sheet after welding. The microhardness of the HSLA steel weld nugget increased significantly (~300 Hv) compared with base material, due to the formation of martensite. However, the slight increase (~18 Hv) in the LCS steel weld nugget was attributed to the formation of austenite, as the temperature in LCS weld nugget was higher than Ac1 while lower than Ac3, austenitizing temperature. Thermal analysis using the SORPAS software revealed that a higher temperature occurred in the HSLA steel compared that in the LCS during resistance spot welding, driving a greater dissolution of Fe into the molten AA5754, leading to the higher microhardness and shear strength of weld nugget in aluminum alloy of the AA5754-HSLA RSWs.