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

Jincheng Nie,Jiqiang Chen,Shengci Li,Changjing Hu,Huilong Zhong,Renguo Guan,Xiangsong Lin

doi:10.3390/met10091145

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.

Highlights

With the development of lightweight technology, the requirements for automotive materials are becoming more stringent in order to make vehicles more energy-efficient and ensure the safety of passengers
Typical columnar crystals which were perpendicular to the fusion line were observed, as indicated by the blue arrows
This is because the growth rate of columnar crystals is characterized by anisotropy, the growth rates vary in because the growth rate of columnar crystals is characterized by anisotropy, the growth rates vary in different crystallographic directions, and tend to grow along the fastest direction of heat dissipation, different crystallographic directions, and tend to grow along the fastest direction of heat dissipation, which should be perpendicular to the isotherm [15]

Summary

Introduction

With the development of lightweight technology, the requirements for automotive materials are becoming more stringent in order to make vehicles more energy-efficient and ensure the safety of passengers. Aluminum alloy has become the preferred material for the alternative structural steel in the automotive industry because of its low density, high strength, good weldability, and corrosion resistance [1,2,3]. It is unavoidable to adopt welding technology for automobiles due to their complex structure. Laser welding, characterized by high energy density, is widely used in the automotive industry [4]. Vehicles are inevitably subjected to high strain rate loading during their service. It is of great importance to study the high strain rate behavior of aluminum alloy welded joints

Methods

Discussion

Conclusion