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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.

To aid in better assessing the corrosion performance of AZ91 die cast magnesium, standard salt spray corrosion tests have been made on both randomly selected commercial die castings and on three series of controlled purity test panels. The results reveal that the poor performance often associated with magnesium parts in salt spray are due principally to iron, nickel, and copper contamination levels. When these contaminants were limited, severe pitting corrosion was eliminated and the salt spray performance was good to excellent when compared to 380 aluminum and cold rolled steel.

Standard salt spray corrosion tests have been used with die cast AS41 samples of controlled purity to define the critical iron, nickel, and copper contaminant levels, up to which excellent corrosion performance can be obtained, and beyond which the corrosion rates accelerate rapidly. As previously observed with magnesium alloys AZ91 and AM60, the critical iron content is dependent upon the manganese content of the alloy, so that the critical factor is the iron:manganese ratio rather than the iron alone. While the iron:manganese tolerance is lower for the AS41 alloy, the tolerance for the nickel and copper contaminants lie between those of AZ91 and AM60. When each of the contaminants is less than the critical level, the salt spray corrosion performance was found to be equal to or better than that of die cast 380 aluminum. This represents a dramatic improvement over that normally associated with AS41 alloy in the past.