No abstract

This paper discusses the effect of several variables in plasma spray method, namely; the flow rate, spray distance and power used on the mechanical properties of Cu-Ni coated A7075. All spraying techniques were designed using 23 factorial plans prior to the actual experiments. The produced coatings were characterised using a scanning electron microscopy (SEM). Morphological observation indicated that most sprayed particles were formed in splash shape splats. The effects of interactions between the response variable factors were screened using a response surface methodology. Three coating factors were used, namely, plasma power, number of coating layer and spraying distance where as the coating hardness and surface roughness were set as the responses. In general, an ideal parameter of 5 coating layers with a power of 30 kW and a spraying distance of 150 mm gave a maximum hardness of 622 Hv and a minimum surface roughness of 9.7 µm.

This work aims to characterise a Cu-based coating material on Al-7075 by using a plasma-spray technique in order to enhance the surface properties of components for automotive applications. Plasma-spray is a process for formation coating on substrates whereby a feedstock is rapidly heated to a molten or near-molten state, and a gas are use to propel the material toward suitably prepared substrate. The most prominent advantages of this method are virtually any coating material can be used and any substrate material can be coated with low thermal stress on substrate parts and high deposition rates [1]. The coating characteristic can be controlled by varying the process variables such as input powers, material feed rates, gas pressures, surface preparation of the substrate and spray distance [2]. The effect of crucial parameters like the electric power input to plasma, spray rate and substrate roughness were studied. The experiments of spraying were design using a 23 fractional factorial plan. The plan allows studying the effect of each factor on the response variables, as well as the effect of interactions between factors on the response variable at the least number of experiment runs. The coating layers have been characterised with respect to the structure by using a scanning electron microscopy (SEM). The result indicates that sprayed particles cool and built up into pancake-like shapes splat, characteristic a plasma spray electric process products. It was found that the optimum parameters were obtained at a power of 24.6 kW, with a powder feed rate of 1 rpm and substrate roughness of 0.5µm.

Despite of its poor tribological properties (low hardness and low resistance to friction, wear and abrasion as well as poor seizure resistance), aluminum has become a potential material in automotives, particularly in the engine areas. To overcome these weaknesses and increase the engine lifetime, a good surface treatment can be one of the best options. In this work, Cu-Ni alloy that has such excellent properties like ductility, corrosion and wear resistance, good electrical and thermal conductivity as well as it can be easily joined or fabricated into useful shapes, was chosen. The work aims to study the wear behavior of Cu-Ni coatings deposited on Al7075 substrates using an atmospheric plasma spray (APS) with different level of plasma powers. Lubricated wear test were carried out on a pin-on-disc tester under an applied load of 100 N with a fixed sliding speed of 0.851 ms-1 at room temperature (~ 23°C). It was found that a decrease in plasma power from 40 kW to 30 kW promoted finer microstructures and higher hardness of the coatings, up to 39%. At 30 kW, the splats formation involved high degree of flattening and solidification without many splashes within the structure. At higher power (40 kW), both velocity and temperature of droplets were noted to be increased, resulting rougher coating structures which were most likely due to overlapped splats. In turn, this weakened the bonding strength between splats. In the case of wear, the resistance of Cu-Ni coated Al7075 was found to be increased from ~6 to 18 × 10-5 mm3/Nm, indicating a mild wear regime that was attributed to an increase in the coating hardness.