A Combined Process of Thermal Spraying and Casting for Fixing Hard Wear-Resisting Coating on the Internal Surface of the Cast Products

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The aim of this research is to overcome the difficulty of internal surface spraying. Experimental investigational were carried out to develop a new technique in order to fix the hard wear-resisting coating on the internal surface of small holes such as cylinder wall in the cast products.Thermal spraying technology and casting technology were skillfully combined. The core components, previously coated hard wear-resisting coating by applying thermal spraying process, were builts in a casting mold. The desired coating such as WC-12%Co coating is left on internal surface of the hole on the cast product after removing just the core component from it. WC-12%Co coating produced by the process of high velocity oxygen-fuel flame(HVOF)spraying has a hardness above Hv900, therefore, it provides an effective wear-resisting property for protecting the surface of aluminum alloy cast products. Although HVOF spraying could not deposit the WC-12%Co coating directly on the surface of resin coated sand core, adoption of the supplemental aluminum underlay coating made it possible. Adhesive strengh of the WC-12%Co coating to the AC4B aluminum alloy cast products is 5-10 MPa in shear mode. It was improved to 10-20 MPa by applying overlay coating of Ni-10%Al alloy, preheating of the casting mold and by roughening the Ni-10%Al alloy overlay coating surface. Three kinds of overlay coating materials Ni-10%Al, Cu-10%Al and Zn were experimented. It was revealed that the overlay coating of Ni-10%Al alloy was most effective to strengthen the adherence between WC-12%Co coating and the cast AC4B body.