Microstructure and Mechanical Properties of Laser Welded 6061-T6 Aluminum Alloy under High Strain Rates

Abstract

Laser welding is widely used for the joining of aluminum alloy in the automotive industry, and the vehicles produced are inevitably subjected to high strain rate loading during their service. Therefore, this paper studied the mechanical properties of 6061-T6 aluminum alloy and its laser welded joint at strain rates between 0.0003 and 1000 s−1. Results showed that the microstructure of welded material (WM) was much finer than base material (BM), typical columnar crystals grew perpendicularly to the fusion line, and the minimum hardness value (~56 HV) was obtained inside WM. The strength and dynamic factors of BM and WM increased with increasing strain rate, and the strength of WM was less sensitive to strain rate compared with BM. The strain rate effect was not homogenous in the plastic deformation region. The modified Johnson–Cook (J–C) model which introduced the term C = C1 + C2·ε could well describe the dynamic plastic deformation of BM. However, the fitted results of the simplified J–C model were overall better than the modified J–C model for WM, especially for high strain rate (1000 s−1). These findings will benefit the determination of the dynamic deformation behavior of laser welded aluminum alloy under high strain rates, and could provide a better understanding of lightweight and the safety of vehicles.