Prestrain and Aging Treatment to Improve the Mechanical Properties of AA6022 Aluminum Alloy Laser Weldment

This study aimed to improve the mechanical properties of aluminum alloy sheet laser weldments. Different tensile prestrains, which simulate sheet forming, were applied to a base metal and its Nd:YAG laser weldment, respectively; then, some samples were subjected to a paint-bake-cycling (PBC) process and some samples were subjected to an artificial aging treatment of 175 °C/1000 min. The tensile test and Vickers hardness test, followed by transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS), and electron-probe microanalysis (EPMA), were applied to examine the microstructures and compositions. The results showed that tensile prestrain and heat-treatment conditions affect the mechanical properties in relation to the different strengthening mechanisms involved. Compared to traditional PBC processes of auto-body panel production, a weldment applied with an artificial aging treatment at 175 °C/1000 min could significantly improve the yield strength and hardness through its precipitation strengthening mechanism. This operation process also reduces the property mismatch between the base metal and weldment. Although the elongation ratio of the weldment is typically inferior to the base metal, the sheet forming process (as prestrain) can be operated on the weldment successfully, while leaving some elongation capability for auto-body panel. Therefore, the proposed aging treatment for the weldment provided in this article is a promising technique.