Tension and shear tests have been carried out to clarify the effects of surfacetreatments of carbon steel and stainless steel on the bonding strength of gassprayed aluminium castings on them. Surface treatments of steels used in thisinvestigation consisted of polyshing by emery paper， sand blasting and acidpickling respectively. In addition， effect of Ni-Al undercoating which sprayedafter above treatments was tested.Aluminium coatings sprayed on the surfaces polyshed by emery paper and acidpickled were easy to peel off from steel surfaces during spraying and Ni-Alundercoating was useful in order to improve on bonding strenngth. Thikness ofthis undercoating was enough at most O. 05mm. Due to this undercoating， carbonsteel polyshed by sand blasting and stainless steel pickled in acid were establishedstrong bonding strength. These treatments generated on the surface of steel theoptimum pitting shapes which provided sprayed aluminium with anchoring effect.Bonding strength of coating was highly increased by the use of annealing processafter deposit.
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