Laser cladding of yttria partially stabilized ZrO2 (YPSZ) ceramic coatings on aluminum alloys

A feasibility study of laser clad 7 wt.% yttria partially stabilized zirconia ceramic coatings undoped or doped with 2.5 wt.% TiO2 to produce single tracks and partially overlapped tracks on the surfaces of AlSi9Cu3, AlZn10Si8Mg and AlSi10Mg alloys was carried out by using a 6 kW RS5000 continuous wave CO2 laser together with continuous powder-feeding system. The dependencies of the macro and microquality of ZrO2 ceramic coatings on the properties of the coating powder and laser parameters, and microstructure (such as morphology, phase transformation, etc.) were studied. The addition of 2.5 wt.% TiO2 into the YPSZ powder is beneficial for the controllable cracking in the ceramic layer on AlSi9Cu3 alloy. The ceramic layers on three kinds of aluminum alloys exhibit planar ZrO2 crystals with different sizes at the lower, columnar grains in the intermediate, and equiaxed grains at the upper region of the cross-sections. Small amounts of molten aluminum alloy are observed to segregate at the boundary regions of columnar or equiaxed grains in the ZrO2 layer because of the poor affinity. The ceramic layers consist mainly of non-transformable t' phase and small amount of the retained c phase. Under conditions of optimum laser parameters and coating powder properties, the bonding to aluminum alloys is satisfactory with small dilution. Molten aluminum alloy is also observed to flow into the cracked ZrO2 layer at the bottom to seal these cracks. The hardness of the ZrO2 ceramic layer was 1415–1575 HV0.1, which is mainly attributed to the absence of porosity and fine grains in the ceramic layers.