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The evolution of microstructure in a Mg 3.4%AI-0.16%Zn-0.33%Mn alloy tube was studied during deformation by ring hoop tension testing (RHTT). When the tests were carried out at moderate temperatures and relatively high strain rates, the accompanying c-axis strains were mainly accommodated by twin formation. At temperatures above 200°C and the lowest strain rate (0.001s-1), the formation of voids in the partially dynamically recrystallized regions caused premature fracture. The microstructural development in hot gasformed samples was similar to that observed during RHTT testing. These results indicate that RHTT testing is an effective way of studying the deformation behavior of Mg alloys during tube gas forming.

Solidification paths and phase stability have been investigated in the creep resistant Mg-Al-Ca based alloys for powertrain applications. The liquidus projection and isothermal sections of the Mg-Al-Ca ternary system were determined, including a ternary (Mg, Al)2Ca intermetallic compound. The solidification of the alloys in the α-Mg primary phase field involves L→α+(Mg, Al)2Ca eutectic reaction in a wide range of compositions and is terminated with invariant reactions that form Mg2Ca or Mg17Al12 phases. The (Mg, Al)2Ca is a high temperature phase and decomposes into Mg2Ca and Al2Ca phases between 773 and 673 K, but the transformation is kinetically quite slow at temperatures below 473 K. Based on this new knowledge, alloy modifications through quaternary elemental additions to improve the solid-solution strength and aging treatments to reinforce the α-Mg phase with precipitates have been demonstrated.

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.

In this paper, the mechanical properties, structural performance and mass saving potential of wrought magnesium alloys are compared to several major automotive materials: mild steel, advanced high-strength steel, cast and wrought aluminum, cast magnesium, plastics and fiber-reinforced composites. Manufacturing processes including welding and joining of magnesium extrusions and sheet products are critically reviewed. The current and potential applications of wrought magnesium alloys in automotive interior, body and chassis areas are discussed. Technical challenges and research opportunities for these applications are identified.

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.