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A methodology that includes the processing history of the metal in the High Pressure Die Casting (HPDC) process in the simulations of the structural behavior of magnesium components has been established. In this methodology the results from the HPDC process simulations are used to modify the material model and the fracture criterion in the Finite Element Analysis (FEA). This paper focuses on the simulation of the HPDC process for thin-walled magnesium components. The close connection between the processing history and the mechanical properties of the casting mandates a careful analysis of the key factors influencing the final part performance. The definition of the boundary and initial conditions will strongly influence the ability to predict important features in the microstructure of the casting and consequently the final mechanical properties of the casting.

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.

The compatibility of magnesium die casting alloys with commercial automatic transmission fluids was studied in laboratory tests. The effects of high temperature, presence of water, and galvanic coupling with steel were examined, using visual observation, weight change, Scanning Electron Microscope, and Scanning Auger Microprobe surface analysis. No significant corrosion of magnesium was detected under any of the test conditions.

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.

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.

Test specimens of magnesium alloys with two, five, six and nine weight percent aluminum were produced by high pressure die casting. The results of room temperature mechanical tests were combined with data from prior investigations to provide property trends as a function of aluminum content. The strength and ductility properties of these alloys generally show opposite dependencies with a change in the aluminum content. Design engineers must therefore make material selection decisions based upon the best balance of properties available for the intended application.

By selecting the right combination of alloy and processing method, a wide range of temperature exposed drive train parts can be made out of die cast magnesium, including engine blocks and automatic transmissions as probably the most demanding components. Successful new alloys for these purposes must fulfill a multitude of requirements to offer a viable solution, including mechanical properties, corrosion properties, die castability and recyclability. Therefore, selection of alloys must be based on the customers' requirements, at the same time as other factors are optimised. In this paper, results from the ongoing alloy development work by Hydro Magnesium are presented, focusing mainly on creep resistant alloys within the Mg-Al-RE system. High temperature tensile data, tensile creep-, stress relaxation- and bolt load retention results from a selection of AE alloys and reference alloys are presented.

This paper reviews the current strategies for physical prototyping of Magnesium instrument panel (I/P) structures. Bottlenecks in the traditional physical prototype based product development process are discussed. As demand for fast-to-market and cost-reduction mounts, virtual prototyping becomes increasingly important in meeting the timing and performance goals. A virtual prototyping methodology is presented in this paper to enable high performance Magnesium I/P structures in Safety, NVH, and initial part quality aspects. Examples of Finite Element Analysis (FEA) results and correlations are included.

High pressure die casting is characterized by rapid die filling and subsequent rapid cooling of the molten metal in the die. These characteristics are favourable for magnesium die casting alloys. The high cooling rate favours the formation of a fine dendrite and grain structure, which in turn leads to substantial hardening; this refinement also provides improved ductility. Since the cooling rate of the metal is highly dependent on both the process parameters and the geometry of the part, the three-dimensional flexibility associated with the latter factor means that the cooling rate cannot be uniform. This cooling rate difference in turn can lead to some variation in the mechanical properties between geometrically different portions of a die cast component. This variation is an inherent property of the material, in contrast to casting defects like microporosity, non-metallic inclusions, filling defects, and formation of hot cracks.

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 advancements and expanded usage of magnesium by the automotive industry are highlighted in this publication which contains 46 SAE Technical Papers presented by technology experts at SAE events from 2001 -2005. This information will aid in improving processes, developing new applications, and identifying new technologies to further the competitive edge of magnesium as a lightweight, recyclable, and viable metal to meet global automotive needs. An increased awareness of the benefits ands features of this light weight structural material has opened a wide range of applications within the automotive industry. Examples include instrument panel structures, seat frames, center consoles, transmission cases, front-end and radiator support structures, and hybrid magnesium powertrains. The advancement continues toward developing even higher-performing alloys to further the competitive edge of magnesium.

The current strong interest in magnesium alloy die castings for automotive applications relies heavily on the “High Purity” concept. The basic knowledge of the detrimental effects of heavy element impurities on the general corrosion of magnesium alloys has been known for more than 60 years. However, it was not until the 1980's that the full potential of high purity alloys was recognized. The level of impurities (in particular, copper, nickel and iron) that can be tolerated in a die cast part exposed to a corrosive environment necessitates careful control throughout the complete manufacturing process, from ingot to finished product. In the present paper, some basic principles for the production of high purity alloys and the influence of subsequent melt handling practice in the die casting shop are discussed.

Selected metallic platings and insulating coatings on steel fasteners were evaluated for ability to reduce galvanic corrosion of die cast magnesium in a modified salt spray test. Proprietary electroplate systems based on zinc, zinc-nickel, zinc-cobalt and tin-zinc were tested, along with a commercial 50-50 tin lead alloy electroplate without supplementary coating. A proprietary liquid-applied zinc-rich inorganic coating successfully used on automotive fasteners was also tested for compatibility with magnesium. Encapsulation of bolt heads with plastic insulating coatings or special molded caps was evaluated. Interruption of the continuous salt spray by rinse and bake cycles was investigated as a likely exposure condition for magnesium assemblies in powertrain or underhood applications. Several of the protection schemes were found to effectively eliminate galvanic corrosion of the magnesium.

High pressure die casting is characterised by rapid die filling and subsequent rapid cooling and solidification of the metal in the die. These characteristics are favourable for the mechanical properties of magnesium die casting alloys. Since the filling pattern and the cooling rate of the metal is highly dependent on both process parameters and geometry of the part, there is a natural variation in mechanical properties. Variations in filling pattern can be caused by differences in the filling conditions set up by the gating system, pre-solidification in the shot sleeve and during filling as well as variations in the timing of the pressure intensification. In the present work the effects of solidification during filling are discussed with emphasis on the resulting microstructures and the correlation with mechanical properties.

The development of creep resistant alloys for automotive drive train components has proven to be metallurgically challenging. This paper discusses the principles of high temperature alloy development, featuring metallurgical, microstructural and processing aspects of some alloys, relative to their high temperature performance. The creep resistant alloys within the Mg-Al base system obtain their creep resistance by a relatively low content of Al, and addition of elements that form stable intermetallic phases within the grain mantle. Various third elements affect the high temperature performance differently. The results demonstrate that rare earth elements (RE) show a remarkable potential as the third element(s).

Near net-shape casting of magnesium matrix composites provides an interesting opportunity to expand the applications of cast magnesium products. In this work, squeeze casting was used to evaluate a series of different short fiber preforms infiltrated with a matrix of high purity AZ91 alloy. Reactions between the fibers and 1) the binder in the preform, and 2) the liquid alloy were examined by metallography and related to the infiltration sequence. Short fibers of Al2O3 (Saffil RF grade) were found to be the most promising reinforcement, based upon the structure and tensile properties of Saffil-reinforced AZ91 alloy at both room and elevated temperature.

This paper describes the methodology by which a combination die cast magnesium and extruded aluminum door frame was developed using a current production steel door design as the base model for comparison. Product performance data, such as side impact requirements and overall door stiffness, along with the packaging of existing internal hardware, is presented. The results are verified by computer modeling. A prototype casting was produced to validate and compare castability requirements and geometry constraints of the door frame. An economic study is included that investigates the potential of developing such a system suitable for production. The results suggest that economic benefits may be obtained by using such a lightweight door system compared to an existing steel door design.

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.

During the last several years the use of magnesium die-castings for automotive applications has been on the rise. Magnesium's use in die-cast form has been expanding at an average growth rate of more than 15% a year. Reasons for the increase are both practical and economic. Magnesium die-castings offer components having the lowest mass when compared to almost any other structural material. Magnesium die-alloys exhibit properties that bridge the gap between engineered plastics and metals. The mechanical performance ratios (strength-to-weight and stiffness-to-weight) of magnesium also compete favorably with metals and plastics. Economically, magnesium alloys prices have fallen during the last several years making them extremely competitive with other materials.