PRECOATS FOR ADHESION OF SPRAYED ALUMINUM COATINGS.
MCDONNELL AIRCRAFT CORP ST LOUIS MO
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The adhesion of sprayed aluminum coatings to SAE 4130 steel having sprayed precoats of molybdenum and Type 420 stainless steel was evaluated and the specimens examined metallographically after exposure to 850F for 200 hours and 1000F for 1 hour. Type 420 S.S. precoats depend on mechanical interlocking to a previously roughened surface for adhesion. Molybdenum, due to its high temperature during spraying, alloys with the surface of steel and provides satisfactory adhesion to SAE 4130 steel with a surface finished to better than 125 rms. Sprayed molybdenum precoats appear promising in bonding sprayed aluminum coatings to steel parts for protection in service environments involving temperatures between 500 - 900F. The precoat appears to bond on steel surfaces without requiring roughening operations that could be deleterious to fatigue properties and no intermetallic formation was observed upon exposure to elevated temperatures. Author