1989-02-01

Field Corrosion Performance of Magnesium Powertrain Components in Light Truck 890206

Field inspection of 41 vehicles equipped with magnesium clutch housings or transfer cases was carried out after service in Nova Scotia or Prince Edward Island for periods up to five years. This area is reported to be the most severe location in North America for salt-induced corrosion of automobiles. The die cast magnesium components were unpainted, but basic measures were taken to control galvanic corrosion.The clutch housings had the longest history, with production spanning the years 1982-1987. The general surface corrosion of these housings was negligible, notably less than that of die cast aluminum 380 or carbon steel components on the same vehicle. Slight galvanic corrosion of exposed bolt bosses was observed, induced by the plated bolt. Some galvanic action was noted at the face-to-face junction between the magnesium clutch housings and aluminum 380 transmission cases. This was not sufficiently advanced to indicate a threat to component function. No galvanic action between the magnesium clutch housing and the Aluminum 5052 spacer plate at the block end was detected.Transfer case history was limited to the 1987 model year. The five trucks examined had only one winter's service. The magnesium cases showed no significant corrosion, either general surface or galvanic.Some supplementary Salt Spray test results are reported.

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