Effect of Process Parameters on Splat Formation during Impingement of Liquid Metal Droplets over a Cold Substrate

Molten metal droplet impingement is an integral part of droplet based manufacturing processes like spray casting and sprays coating. In these processes, in a single operation, a liquid metal stream is atomized into fine droplets, which impact on a substrate to form a bulk deposit. The properties of casting or coating strongly depend on the shape of splats formed by individual droplets after impingement and solidification. Therefore, considerable research studies have been carried out to characterize individual droplet impact, usually driven by an interest in a particular process. These studies include extensive modeling of droplet deposition, some of which are supported by experimental studies. Most of these modeling activities have focused on the impingement of a droplet on to a surface to predict quantities such as the extent of maximum spread and the final equilibrium diameter, the rate of heat transfer to the substrate, and the solidification rate. Due to interaction of several complex phenomena, comprehensive modeling of the droplet deposition is a challenging task. The flow of liquid droplet upon impingement is itself a complex phenomenon. Heat transfer and solidification occurring concurrently with the flow adds further to the complexity. Thus the present study aims at the development of a comprehensive mathematical model of impingement of liquid metal droplet upon a substrate to understand the effect of process parameters such as initial temperature of droplet, size of droplet and velocity of droplet.

Effect of Microstructure on Wear Characteristics of Spray Cast Al-Si Alloys

In the present study, the effect of microstructure on the wear characteristics of spray cast Al-15Si and Al-20Si alloys has been investigated and compared with that of vertical axis centrifugal cast and chill cast alloys. The spray cast alloys have been subjected to Hot Isostatic Pressing for porosity reduction. HIPing has reduced the porosity in the spray cast Al-15Si and Al-20Si alloys from 19% to 8% and 19% to 2% respectively. The microstructures of spray cast alloys consisted of finely divided globular shaped Si particles with sizes varying from 2–10 µm. The Si particles have been distributed uniformly throughout the Al matrix. On the contrary coarse and segregated microstructures have been observed in vertical axis centrifugal cast and chill cast alloys. The sizes of primary and eutectic Si in vertical axis centrifugal cast alloys are smaller than that in chill cast alloys. The wear rates are the lowest for spray cast alloys and highest for chill cast alloys over a wide range of sliding velocity. The reasons for better wear resistance of spray cast alloys have been discussed in the light of the microstructural features evolved during spray casting.

Research on the Mechanical Properties of Al6061 Intermetallic Compounds Solubility as Manufactured by Spray Casting

Al6061 alloys are well known as extrusion materials for automobile parts, aircraft. Recently, increasing demands of the lightweight for vehicles, materials have replaced steel are developed. Aluminum alloys are increasingly used as structural materials but in terms of mechanical properties, it is not a completed as a replacement for steel. The purpose of this study was to improve the mechanical properties and minimize the grain sizes of Al6061 matrix alloys for structural materials as produced by spray casting. Al6061 alloys were melted with 800°C in electrical resistance furnace. In order to form equilibrium concentration of Mg2Si (about 2 times) for Al6061, increased Mg and Si were added to Al6061 alloys and then preforms were prepared with molten metal by spray casting. The Specimens were fabricated by solution heat treatment and T6 age hardening. As a result of analyzing microstructure observations and mechanical properties according to supersaturated solid solution of Mg2Si for the final sample obtained, there were no changes in the size of the precipitates but precipitates per unit area were found to increase the area during the heat treatment processes. Mechanical properties such as tensile strength of over 80MPa and hardness of over 10HRB in spray casting have been increased according to solubility of Mg2Si.