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Technical Paper

A Review of the Life Cycle Environmental Performance of Automotive Magnesium

The use of aluminum and magnesium provides cost-effective weight savings in car components. Its increased use, as a structural and body material will bring about further weight savings. Environmentally this translates into fuel savings and lower emissions. Substituting light metals as magnesium and aluminum for steel in the primary structure of a car opens up room for design innovation and changes in production processes tailored to the particular needs of automotive industry. Additionally sophisticated recycling techniques are needed, i.e. recycling of the light weight metals from ELV's must be efficient in terms of amount recovered and material properties. The aim of this paper is to review various Life Cycle Analyses (LCAs) conducted over the last years for environmental assessment of automotive parts made of light metals. Use of SF6 and recycling effects are highlighted. The advantage of using magnesium and aluminum is obvious when using the car.
Technical Paper

Behavior of Die Cast Magnesium Alloys Subject to Rapid Deformation

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.
Technical Paper

High Purity Magnesium Die Casting Alloys: From Ingot to Cast Product

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.
Technical Paper

Metal Quality - The Effects on Die Casters and End Users

As more and more magnesium metal is used and recycled, particularly for safety-sensitive components, the maintenance of metal cleanliness remains of critical importance. The term metal quality may be defined as 1) chemical composition 2) inclusions and porosity inside the metal, 3) the surface appearance and 4) consistency. This definition may apply to both ingots and cast parts. Chemical composition of ingots will influence on the cast parts, but also process operation at the die casters' will contribute to the chemical composition of the final product. The inclusion contents of a cast component is only indirectly determined from the cleanliness of the ingots from where it origins, emphasising the need for metal cleanliness assessment in the die casting shop. Beside the die casting process itself, the ingot surface appearance and the housekeeping in the die casting furnaces are important for the property of the product.
Technical Paper

Non-Chromate Conversion Coatings for Magnesium Die Castings

Hexavalent chromium-containing baths have traditionally been used as pre-treatments on magnesium alloys. Environmentally friendly alternatives to these baths are being investigated. One alternative seems to be a phosphate-permanganate treatment consisting of a mixture of sodium dihydrogenphosphate and potassium permanganate. The phosphate-permanganate treatment has shown equivalent performance to a standard chrome pickle, both as stand-alone corrosion protection and as a base for subsequent coating. Phosphate-permanganate treatments must be combined with a deoxidizing process to be successful. Another alternative is a fluorozirconate treatment. The paint base properties of fluorozirconate are quite close to what is obtained using a chrome pickle.
Technical Paper

Powertrain Components - Opportunities for the Die Cast AE Family of Alloys

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.