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<p>Cold metal transfer (CMT) welding process, known for its precision and low heat input, is a preferred technique for the joining of thin sheets, and therefore, it is a promising method for the fabrication of battery trays used in electric vehicles (EVs). This study investigates the influence of CMT process parameters on the weld quality, microstructure, and mechanical properties of 1.5-mm-thick AA6061 alloy in butt joint configuration with and without post-weld heat treatment (PWHT). Microstructural analysis showed dendritic structures in the fusion zone (FZ), with columnar grains near the FZ–heat-affected zone (HAZ) interface. The HAZ exhibited equiaxed grains, while the base metal (BM) displayed elongated grains along the rolling direction with Mg<sub>2</sub>Si particles at the grain boundaries. Optimal welding parameters (50 A current, 4&#xa0;mm/s travel speed, and 2.0&#xa0;mm arc length) produced defect-free welds with excellent bead geometry and mechanical performance, achieving a weld efficiency of 95%. This study also evaluates the positive effect of PWHT on weld joints relevant for lightweight EV structures. PWHT further improved the joint properties by increasing the microhardness of HAZ by approximately 40% along with a 20 % improvement in elongation (%), which was attributed to the re-precipitation of Mg<sub>2</sub>Si particles. EBSD analysis showed that BM had a finer grain structure (20 ± 2.2&#xa0;µm) compared to FZ (34 ± 2.4&#xa0;µm), indicating significant grain coarsening due to the thermal cycle of welding. Scanning electron microscopy (SEM) with energy-dispersive x-ray (EDX) and XRD confirmed the presence of Mg-, Si-, Fe-, and Cu-based secondary phase particles that improved the hardness as well as the strength of the welded joints. The combined process notably enhances joint strength and ductility in thin aluminum sections, demonstrating its suitability for high-performance welds in EV battery housings.</p>

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Enhancing Cold Metal Transfer Welded Aluminum Joints with Post-Weld Heat Treatment for Electric Vehicle Battery Tray Applications

  • 期刊论文

  • 发表日期：

    2025年9月29日

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  • Rukaiya Azma,
  • Aviral Rastogi,
  • Shewtank Rai,
  • Naveen Kumar,
  • Abhishek Das

摘要

Cold metal transfer (CMT) welding process, known for its precision and low heat input, is a preferred technique for the joining of thin sheets, and therefore, it is a promising method for the fabrication of battery trays used in electric vehicles (EVs). This study investigates the influence of CMT process parameters on the weld quality, microstructure, and mechanical properties of 1.5-mm-thick AA6061 alloy in butt joint configuration with and without post-weld heat treatment (PWHT). Microstructural analysis showed dendritic structures in the fusion zone (FZ), with columnar grains near the FZ–heat-affected zone (HAZ) interface. The HAZ exhibited equiaxed grains, while the base metal (BM) displayed elongated grains along the rolling direction with Mg2Si particles at the grain boundaries. Optimal welding parameters (50 A current, 4 mm/s travel speed, and 2.0 mm arc length) produced defect-free welds with excellent bead geometry and mechanical performance, achieving a weld efficiency of 95%. This study also evaluates the positive effect of PWHT on weld joints relevant for lightweight EV structures. PWHT further improved the joint properties by increasing the microhardness of HAZ by approximately 40% along with a 20 % improvement in elongation (%), which was attributed to the re-precipitation of Mg2Si particles. EBSD analysis showed that BM had a finer grain structure (20 ± 2.2 µm) compared to FZ (34 ± 2.4 µm), indicating significant grain coarsening due to the thermal cycle of welding. Scanning electron microscopy (SEM) with energy-dispersive x-ray (EDX) and XRD confirmed the presence of Mg-, Si-, Fe-, and Cu-based secondary phase particles that improved the hardness as well as the strength of the welded joints. The combined process notably enhances joint strength and ductility in thin aluminum sections, demonstrating its suitability for high-performance welds in EV battery housings.