SPRAY FORMING AND CHARACTERIZATION OF COLD ROLLED AI-Pb ALLOY

Abstract

Processing of Al-Pb alloys by the conventional casting techniques is difficult due to liquid immiscibility and segregation of lead during melt solidification. To overcome these problems, spray forming can be used which also possesses several advantages like microstructural control together with producing a near net shape perform in a less number of processing steps In this experiment a convergent-divergent nozzle used to atomize the melt. Then Al-Pb alloys were spray formed in the form of a disc shape by using this nozzle and their characteristics such as microstructure, porosity, hardness wear etc were studied. The spray droplets were deposited over a copper substrate to achieve a disc shape preform. The porosity, hardness, wear and microstructural studies of the Al-Pb spray deposited alloys were conducted for 20% lead content in aluminum after the cold rolling process for 20% , 40%, 60% and 80% of the thickness reduction from middle and peripheral regions and Optical micrographs were taken for the samples with different percentage of thickness reduction from middle and peripheral regions. In scanning electron micrograph the grain boundaries were clear with the 20% of the lead content and max amount of lead content was distributed along the grain boundaries. The lead was uniformly dispersed in the deposit as revealed by color dot map. The surface porosity and total porosity increases with increase in the percentage of the reduction in thickness of the samples. The hardness increased in middle and peripheral regions due to increase in the percentage of reduction in thickness of the samples. Friction and wear testing of spray formed alloys were investigated using a pin on disc type wear testing machine .wear rate behavior with applied load was observed i.e. wear rate increased with increasing the load . And the coefficient of friction decreases rapidly up to the load of 30N and beyond this load the coefficient of friction was almost constant.