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Technical Paper

The Effect of Non-Metallic Inclusions on the Properties of Die Cast Magnesium

The effect of non-metallic inclusions (NMIs) on the properties of die cast magnesium was investigated. NMI content was quantified by a newly developed light reflectance technique. The mechanical properties of optimized AM60B test bars were found to decrease at high inclusion levels. Low inclusion levels did not statistically reduce the mechanical properties of AM60B as compared to virgin metal. Argon-refined AM60B displayed mechanical properties that were indistinguishable from virgin alloy. AZ91D test plates were die cast at various cleanliness levels. After salt spray testing, it was found that the surface quality of the castings was slightly degraded at high NMI levels. The general corrosion performance was also affected, but paint adhesion was relatively unaffected. At high NMI levels, the corrosion performance was still better than 380 A. Machinability of the AZ91D test plates was quantified by measuring tool wear and cutting forces.
Technical Paper

The Critical Contaminant Limits and Salt Water Corrosion Performance of Magnesium AE42 Alloy

The magnesium alloy AE42 (nominally a 4 % aluminum, 2 % rare earth alloy of magnesium) is a developmental die cast alloy with good strength and creep resistance at elevated temperatures. Standard salt spray corrosion tests have been used with controlled purity AE42 die castings to define the critical iron, nickel and copper contaminant levels below which excellent corrosion performance can be obtained. As previously observed with the magnesium alloys AZ91, AM60, and AS41, the critical iron content is dependent upon the manganese content of the alloy. While the iron:manganese tolerance for AE42 is about the same as that of AM60, the tolerance for the nickel and copper contaminants is greater than that of AZ91. When each of these contaminants is less than the critical level, the salt spray performance was equal to or better than die cast 380 aluminum and cold rolled steel.
Technical Paper

Separation of Non-Metallic Contaminants in Fluxless Melting and Refining of Magnesium Alloys

Recent growth in automotive applications of magnesium die cast alloys has made the refining and recycling of magnesium scrap a key issue for the automotive and magnesium industries, if growth is to continue. Today, with only a few exceptions, commercially refined and recycled alloy is produced using a variety of flux-based processes. However, fluxless refining, has been the focus of growing interest, particularly for the in-house refining of scrap by the die cast producers. This paper summarizes the results of a study conducted to better understand the behavior of non-metallic contaminants in scrap melts and the requirements for their separation, using argon sparging. Brightness measurements were used to experimentally determine the distribution of non-metallic contaminants within scrap melts both before and after argon treatment.
Technical Paper

Magnesium Die Cast Alloys for Elevated Temperature Applications

Mechanical testing and prototyping of several developmental magnesium die cast alloys have shown that certain magnesium alloys can be exposed to temperatures in excess of 232°C (450°F) and still have adequate strength. For example, one of the alloys tested at 260°C (500°F) had a tensile yield strength greater than 87 HPa (12.7 ksi). Further testing also revealed that some of these alloys possess better creep strength at 316°C (600°F) than AZ91D has at 177°C (350°F) with at least as good castability as AS41A.
Technical Paper

Extruded Magnesium Alloys Reinforced with Ceramic Particles

Ceramic particle reinforced magnesium alloy billets as large as 70 kg were produced by casting techniques. Extrusion of the composite billets was somewhat more difficult than that of unreinforced magnesium alloy billets; nonetheless, magnesium composite extrusions have been produced in several shapes and a wide variety of compositions. AZ31B + 20 vol. % 600 grit SiC possesses excellent stiffness, combined with relatively good extrudability. Z6 (magnesium - 6 wt. % zinc) + 20 vol. % 1000 grit SiC is substantially stronger than any commercially available magnesium alloy extrusion.
Technical Paper

An Innovative Shot Delivery System for Magnesium

Fast, accurate delivery of metal to the shot well is critical to the success of any cold chamber die casting operation. For some metals this is a simple problem to solve. Magnesium, however, requires more innovative thinking. Simplicity of design is essential for reliable operation in the environment of a magnesium die casting facility. Complex control is required to provide speed and accuracy of shot delivery. Blending these two ingredients to produce a viable system produces a truly innovative shot delivery system for magnesium. Construction details of a newly developed stand alone system for the auto ladling of magnesium will be presented. Data with regard to speed and accuracy will also be presented.