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

本研究的目的是克服内表面喷涂的困难。为了将硬质耐磨涂层固定在铸件气缸壁等小孔的内表面，进行了试验研究。将热喷涂技术与铸造技术巧妙地结合起来。采用热喷涂工艺，在铸造模具中浇注预先涂覆硬耐磨涂层的核心部件。所需的涂层，如WC-12%Co涂层，在仅去除铸件上的核心部件后，留在铸件上孔的内表面上。采用高速氧-燃料火焰喷涂工艺制备的WC-12%Co涂层硬度在Hv900以上，为铝合金铸件表面防护提供了有效的耐磨性能。超音速火焰喷涂虽然不能在树脂包覆砂芯表面直接沉积WC-12%Co涂层，但由于采用了铝衬底涂层，使之成为可能。在剪切模式下，WC-12%Co涂层与AC4B铝合金铸件的结合强度为5~10 Mpa。通过采用Ni-10%Al合金堆焊层、铸型预热、Ni-10%Al合金堆焊层表面粗化等措施，使熔覆层的抗拉强度提高到10~20 Mpa。试验了镍-10%Al、铜-10%Al和锌三种堆焊层材料。结果表明，Ni-10%Al合金堆焊层对增强WC-12%Co涂层与AC4B铸件的结合力最为有效。

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.