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Magnesium and aluminum alloys offer lightweighting opportunities in automotive applications. Joining of dissimilar materials, however, generally requires methods that do not involve fusion. This paper explores the use of self-pierce riveting (SPR) to join magnesium to aluminum alloys for structural and closure applications. The preliminary results indicate that SPR is a viable option for joining aluminum extrusions to magnesium die castings, as well as stamped sheet aluminum to quick-plastic-formed (QPF) sheet magnesium.

Corrosion tendency is one of the major inhibitors for increased use of magnesium alloys in automotive structural applications. Moreover, systematic or standardized methods for evaluation of both general and galvanic corrosion of magnesium alloys, either as individual components or eventually as entire subassemblies, remains elusive, and receives little attention from professional and standardization bodies. This work reports outcomes from an effort underway within the U.S. Automotive Materials Partnership - ‘USAMP’ (Chrysler, Ford and GM) directed toward enabling technologies and knowledge base for the design and fabrication of magnesium-intensive subassemblies intended for automotive “front end” applications. In particular, subassemblies consisting of three different grades of magnesium (die cast, sheet and extrusion) and receiving a typical corrosion protective coating were subjected to cyclic corrosion tests as employed by each OEM in the consortium.

Magnesium alloy extrusions offer potentially more mass saving compared to magnesium castings. One of the tasks in the United States Automotive Materials Partnership (USAMP) ?Magnesium Front End Research and Development? (MFERD) project is to evaluate magnesium extrusion alloys AM30, AZ31 and AZ61 for automotive body applications. Solid and hollow sections were made by lowcost direct extrusion process. Mechanical properties in tension and compression were tested in extrusion, transverse and 45 degree directions. The tensile properties of the extrusion alloys in the extrusion direction are generally higher than those of conventional die cast alloys. However, significant tension-compression asymmetry and plastic anisotropy need to be understood and captured in the component design.

This paper describes the tensile creep and microstructure of Mg-Al-Ca-based ACX magnesium alloys being developed for powertrain applications. Important creep parameters, i.e., secondary creep rate and creep strength, for the new alloys are reported. Tensile creep properties of the newly developed ACX alloys are significantly better than those of AE42 alloy, which is the benchmark creep-resistant magnesium die casting alloy. Creep mechanisms for different temperature/stress regimes are proposed. A new intermetallic phase, (Mg,Al)2Ca, was identified in the microstructure of the ACX alloys, and is proposed to be responsible for the improved creep resistance of the alloys.

Aluminum tube hydroforming offers further mass savings and performance improvement compared to solid stampings and castings. This paper reports the formability of 6063-T4 extruded tubes and 5754 seam-welded tubes. Tensile and fatigue properties of the hydroformed sections are investigated. The results also show that despite its lower yield strength (but higher ultimate tensile strength and ductility), the hydroformed 5754 alloy has higher fatigue resistance than the 6063-T7 material.