Rahool.V. Ramgounda and Ramappa.Savadi
The liquid immiscible alloys based on Al-Pb system are potential materials for application in automobile and aerospace industries. However, their processing by the conventional casting techniques is difficult due to liquid immiscibility in a wide range of temperature and com- position and also large density difference of the constituent phase. In the past, several techniques different from conventional casting have been employed to prevent segregation of lead during freezing of the melt. Techniques based on ultrasonic vibration of melt, powder metallurgy, stir casting, space metallurgy, rheocasting, strip casting, melt spinning and spray forming, results in a uniform distribution of lead particles in Al matrix. However, some of these techniques are often associated with either a higher energy consumption or generation of coarse grain microstructures. Among these techniques, spray forming possesses several advantages in effective micro structural control together with producing a near net shape preform in a less number or processing steps. In this process, the melt is superheated to a temperature above the liquid immiscibility region of the melt prior to atomization. Rapid cooling associated with solidification of atomized droplets and a turbulent fluid flow condition on the deposition surface minimizes the separation of the Al and Pb-rich phases. However, a high melt temperature result in rapid coarsening of Pb particles in this process. The present investigation reports a modification of the spray forming process to avoid coarsening of Pb particles in Al-10Si-10Pb alloys. The micro structural features of the spray formed alloys and their resultant wear characteristics are reported. The wear testing of spray formed alloys were investigated using a pin on disk type wear testing machine. The standard wear test procedure was followed for evaluating the wear rate for different load ranging from 10 to 90 N at a constant sliding speed of 1.0 ms1 . All the tests were carried out in dry sliding conditions and at room temperature. The worn out surface and debris particles were preserved periodically for further examination. The wear rate was observed in the range of 1 to 6.5X10-12m 3m1 and the coefficient of friction was found to be 0.4.