Study case of aluminium die-cast parts with different gating conditions tested in fatigue

Abstract

Aluminium die-castings whose performance needed to be evaluated against the baseline were subjected to fatigue testing. The results showed lower than expected fatigue life and incorrect Weibull distribution of the data, as well changes in the failure location and fracture morphology. This was a clear indication that the casting parameters were inadequate. In addition, the microstructure analysis revealed the presence of flow-induced segregation patterns, entrapped oxide films, gas porosity, microshrinkage and dross. Die-cast parts typically exhibit some of these microstructural inconsistencies; however, in this case, the presence of atypical casting defects such as the numerous internal cold drops and cold shuts in the fracture surface pointed towards incorrect casting parameters and design as root cause. 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. After improvements were made to the gating system, the evaluated castings achieved the desired quality of the baseline parts.