An Evaluation of Quality and Performance of Self-Piercing Riveted High Strength Aluminium Alloy AA6008 for Automotive Applications

Reducing vehicle weight, to improve fuel efficiency and reduce greenhouse gas emissions, continues to be a key objective in the automotive industry. As a result lightweight materials, such as aluminium alloys, are used increasingly for automotive body structures. Currently, self-piercing riveting (SPR) is a major technology used by manufacturers to join aluminium body structures. However, greater demands on the technology present themselves as ever higher strength alloys are required to be joined. The paper reported here focuses on the quality and performance of joints involving AA6008T61, recently introduced for potential applications in automotive body structures. In order to explore the process boundaries, AA6008T61 was supplied with different yield strength values which were obtained through different heat treatment procedures applied by the material supplier. As it is likely that mixed alloy combinations will be required to be joined, body structural aluminium alloy sheet AA5754 with different thicknesses was also be used through this project. The results suggested that SPR is capable of joining AA6008T61 as the top and middle layer with proper rivet/die combination. However, when AA6008T61 was used as the bottom layer, improper selection of die profile could lead to severe cracking. A new type of die with a truncated profile was proved to be able to relieve/improve the cracking situation. The severity of cracking on AA6008 T61 was dependent on the thickness of the top layer and the strength of the AA6008T61 itself. The results show that thinner top material thickness and/or stronger bottom material strength would produce more and larger cracks on the joint button. With the increasing of top material thickness, joint static strengths will increase, and the influence of bottom material strength on joint strength was not significant.