Microstructure Investigation of Aluminum Die-Cast Parts with Different Gating Conditions Tested in Fatigue

Abstract

Aluminum die-cast parts from a foundry being evaluated as an alternate source were subjected to fatigue testing. The results showed lower than expected fatigue life and a change in the failure location of the evaluated parts compared with the baseline parts, which prompted submission of both sets of samples for metallurgical evaluation. Optical microscopy, scanning electron microscopy and non-destructive X-Ray imaging tools were employed to characterize the material and fracture surface. Die-cast parts typically exhibit some level of microstructural inconsistencies, such as micropores or microshrinkage. However, in this case, the presence of atypical casting defects (such as cold shuts) in the evaluated samples pointed toward incorrect casting parameters and design as root cause of the lower fatigue life and change in failure mode. Further investigation determined that a different gating system, more prone to cold shut development — all other parameters being equal, was used to produce these parts.