Dry Sliding Wear Properties of a 7075-T6 Aluminum Alloy\ud Coated with Ni-P (h) in Different Pretreatment Conditions

Dry sliding wear behavior of electroless nickel-phosphorus (EN) coating of thickness �35 lm deposited on\ud a 7075-T6 aluminum alloy was studied. EN was deposited from a bath with sodium hypophosphite as a\ud reducing agent. In as-deposited conditions, plating with 6-9 wt.% phosphorus has a mixture of amorphous\ud and microcrystalline phase. Three pretreatments of Zn (zincate), Ni strike and absorbed hypophosphite\ud layer were given to the substrate before EN coating to examine their wear performance. The surface\ud morphology of the pretreatments was studied by a confocal laser scanning microscope. The performances of\ud these pretreatments of EN were evaluated by dry sliding wear studies and followed by SEM studies. The\ud results suggest that the wear behavior of EN mostly depends on the pretreatment conditions. Heat treatment\ud at temperature of 400 �C can enhance the wear resistance properties for all types of pretreatment\ud conditioned samples and in addition that the average coefficient of friction of 400 �C specimens (lav) had\ud minimum value as compared to 200 �C specimens. Ni strike provided better interlocking adhesion between\ud EN and Al and this pretreatment noticeably improved the wear, frictional and hardness behavior of the EN\ud coatings on 7075 Al substrate and further enhanced it by heat treatment of 400 �C/h