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Investigation of erosive-corrosive wear in the low pressure die casting of aluminum A35 Miller, Ainsley Elizabeth

Abstract

Low pressure die casting is a process commonly used to produce aluminum wheels. Die surfaces are exposed to a wide range of operating conditions, including high temperatures, high local pressures, and varying melt velocity, which can result in erosive-corrosive wear. The sprue is an integral component of the die and channels liquid aluminum into the wheel cavity. Typically sprues are made from steel and have a protective coating applied to the surface to provide insulation from the effects of liquid aluminum. However, flow-related phenomena can prematurely wear away this coating, resulting in accelerated surface wear. Erosive-corrosive wear experiments were performed to investigate the effect of geometry on sprue material wear in liquid aluminum alloy A356. Experiments were performed using a laboratory rotating pin apparatus, similar to other tests in literature, examining the effect of pin geometry, velocity, material, temperature, and time on wear behaviour. A profiled cross-section incorporating features from the sprue geometry was used to evaluate the influence of geometry. To ensure that test velocities were realistic, fluid flow models were developed to simulate die cavity filling during low pressure die casting and velocity profiles along the rotating pin surface. The pins were primarily made from 4140 steel, with two profiled pins made from HI3 steel and titanium alloy Ti-6A1-4V. Additional tests were performed with cylindrical pins to validate test set-up and evaluate the effect of additional parameters. Wear increased with increasing velocity, temperature, and time. The titanium pin showed the least amount of wear, followed by the H13 steel pin. The profiled cross-section produced regions of different pressure and velocity along the surface, promoting accelerated wear at some locations. Most wear was observed along the leading edge of the rotating pin. The flow in the sprue exit region was more closely represented by flow along the pin trailing edge. Along both surfaces, flow simulation predicted a region of flow separation. This region was largest for the 15° pin, which experienced the least wear along the trailing edge and may have implications on accelerated sprue wear. More study needs to be completed in terms of the influence of flow on wear, however, preliminary results suggest that larger pin/sprue draft angles may improve wear performance.

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