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Padded self-piercing riveting (P-SPR) is a newly developed multi-material joining technology to enable less ductile materials to be joined by self-piercing riveting (SPR) without cracking. A deformable and disposable pad was employed to reduce the stress distribution on the bottom surface by supporting the whole bottom sheet continuously during rivet setting process. To verify the P-SPR process, 2.0mm thick 6061-T6 wrought aluminum was joined with 3.2mm thick coated AM60B magnesium high pressure die casting (HPDC) by using 1.0mm thick dual-phase 600 (DP600) steel as the pad. Regular SPR processes with 2 different die geometries were studied as a comparison. Compared to the regular SPR processes, P-SPR demonstrated advantages on coating protection, crack mitigation and joint strength.

As automotive companies increasingly incorporate lightweight materials into the new vehicles to improve fuel economy, development of joining technologies for different material combinations is also required. As a key mechanical fastening technology for dissimilar materials, self-piercing riveting (SPR) has been well established in joining aluminum and steel. However, the application of SPR on magnesium alloys was impeded mainly by the cracking issue resulting from its limited slip-systems at room temperature when magnesium was restricted to be on the bottom due to galvanic corrosion concern. To solve this issue without much modification on existing process, a concept of adding a layer of ductile material underneath of the bottom magnesium to receive the rivet is proposed. An experiment was designed to investigate this concept by joining a mild steel and a magnesium die casting with a ductile aluminum as a rivet receiver.

Historically, accelerated cyclic corrosion test protocols utilized by original equipment manufacturers (OEMs) have been developed based on a great knowledge and abundant vehicle field data of primarily steel-containing vehicle components. Laboratory-accelerated cyclic corrosion tests with repeated cycles of wet, dry, humid, and/or corrosive media application have been developed both separately and in partnerships, such as in the case of SAE J2334, to simulate a severe corrosive field environment for evaluation of cosmetic corrosion performance of painted steel. With the interest in lightweight metals such as aluminum alloys and magnesium alloys in automotive applications, the validity and confidence of these accelerated test protocols with vehicle field data of lightweight metals is valuable to further increasing the usage of these metals.

This paper provides an overview of the research efforts within the AUTO21 program on magnesium die-casting. The objective of the program is to better understand the mechanical properties of magnesium high pressure die-castings (HPDC) and to develop the capability to predict the local mechanical properties over a given component based on its shape, the design of the mold and the casting parameters used in its production. The paper highlights the research group's findings related to the microstructure and mechanical properties of a full-scale instrument panel beam casting and outlines the goals of the continuing research program.

The robustness of large magnesium thin wall die castings has been proven through testing performed directly on components and supported by statistical analysis of the test data. In addition, an extensive investigation carried out on specimens cut from components tends to show that the material exhibits a composite failure mode. The skin shows high consistent elongations close to the intrinsic potential of the alloy, while the core properties vary with the micro-defects inherent to the process. Design data has therefore been developed by reverse engineering from component tests, considering local properties and loading mode.

With rapid growth of magnesium alloy applications in automotive industry, especially for external components, corrosion prevention is becoming increasingly important. It is necessary to evaluate coating systems that are applied on magnesium prior to component assembly. Furthermore, the interaction between coating systems and methods for galvanic corrosion prevention should be considered carefully. The present paper discusses the methodology for corrosion protection of external automotive components and demonstrates some examples of technical solutions.