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Designing for fatigue performance requires extensive knowledge of material properties, component geometry and dynamic loading conditions. These topics are addressed in an ongoing cohesive research program on fatigue behavior of magnesium die castings. The current phase of the program includes effects of alloy type, mean stress level, surface condition, and level of tensile properties. The results, presented as S-N curves and Goodman diagrams, show a significant difference in the fatigue life between AZ91D and the AM alloys. Fatigue behavior of AM60B was strongly dependent on the mean stress level, but was not significantly influenced by a minor difference in casting quality. The fatigue behavior of AM50A was not noticeably changed by the addition of vibratory polishing.

The phenomenon of stress relaxation in a solid corresponds to a time-dependent decrease in stress under given constraint conditions. An apparatus for stress relaxation compression testing was constructed and utilized to evaluate a series of die cast magnesium alloys. The behavior of the alloys was determined over a 100 hour test period. In general, the percentage of stress remaining after this time decreased with increased initial stress and with increased test temperature. Of the materials tested, magnesium alloy AE21 showed the best relaxation resistance relative to 383 aluminum alloy.

The development of magnesium for components which must withstand appreciable loads at elevated temperatures must be accompanied by an expanded material properties database. Tensile, creep and stress relaxation properties are among those particularly needed to provide automotive product engineers with proper information to design in magnesium. This paper provides a compilation to date of property data which are being generated in ongoing research and development programs. Magnesium alloys from the AE and AS series are particularly emphasized.

The development of commercial magnesium die casting alloys has progressed over the past several decades. The most common die casting alloy, AZ91D with 9% aluminum content, has been and still is used in many structural automotive applications. New magnesium alloys have been developed in the past several years to meet the needs of structural applications that require an appreciable amount of energy absorption during service. Magnesium alloys having lower aluminum content, such as AM50 and AM20, were developed by Norsk Hydro and found to be more ductile, especially during impact situations. Their immediate use was focused towards applications such as automotive seat frames and instrument panel/cross-car beams. This paper provides mechanical property data on the “AM-Type” magnesium alloys. These alloys consist primarily of aluminum and manganese additions to magnesium to increase the energy absorption attributes of the base metal.

The development of commercial magnesium die casting alloys has progressed over the past several decades. The most commonly used die casting alloy, AZ91D, with 9% aluminum content, has been and still is used in the majority of structural automotive applications. New magnesium alloys have been developed in the past several years to meet the needs of structural applications that require an appreciable amount of creep resistance and improved stress relaxation performance during service. Typical applications would include powertrain components. This paper provides further mechanical property data on the “AE-Type” magnesium alloys. These alloys consist primarily of aluminum and rare-earth additions to magnesium to increase creep resistance and stress relaxation performance attributes of the base metal. However, changes in tensile strength, elongation, etc. may also be realized.

Magnesium alloy die castings provide opportunities for designing low weight, cost efficient solutions based upon a fully recyclable material. These incentives are highly attractive for the automotive industry. It should be emphasized that the majority of published and tabulated data on properties of magnesium die castings does not reflect the recent advances in alloy chemistry and die casting technology. In the present paper a summary is presented of mechanical and physical data of magnesium die casting alloys. The properties are representative for test bars produced under well controlled conventional cold chamber casting conditions. It should be stressed that further refinement of the casting technology (vacuum assisted casting etc.) can further enhance the mechanical properties. Fatigue properties are still under evaluation and will be reported separately.

he mechanical properties of magnesium die castings that are critical to the design of interior components are evaluated in three situations. First, the results of instrumented impact testing of the AM alloys, AZ91D and AE42 are reviewed. Second, creep properties of AZ91D and the AM alloys at a slightly elevated temperature, 50°C, are evaluated. Lastly, the effect of aging at 100°C on the AM alloys is reported. In all cases, the results are based on separately cast test bars.

The effect of strain rate on tensile properties of cold chamber die cast AZ91D, AM60B and AM50A test bars is reported. The strain rate was varied from 15 s1- to 130 s-1, a range typical of deformation and crash. All tests were done at room temperature. The properties measured include fracture elongation and ultimate tensile strength values. The results are discussed in terms of the work hardening characteristics and strain rate sensitivities of the materials, and parameters in a material model suggested by Johnson-Cook have been determined. It has been found that flowstress increases and that elongation is not affected by strain rates from 15 s-1 to 130 s-1. The energy absorption during deformation increases therefore with the speed of deformation, emphasizing the positive properties of magnesium die cast alloys for safety related applications.