Improved mechanical properties in vacuum-assist high-pressure die casting of AZ91D alloy

Significantly improved mechanical properties of the AZ91D alloy, i.e., similar to 20% higher ultra tensile strength, double elongation and treble low-cycle fatigue life, were achieved by employing a specially designed flow distributer during the vacuum-assist high pressure die casting (HPDC) process. The application of vacuum in HPDC could significantly improve the mechanical properties of the components by reducing the gas pores. In addition, by employing the specially designed flow distributor, the external solidified crystals (ESCs) could be effectively blocked from entering the die cavity, which significantly reduced the magnitude scattering of the mechanical properties. By applying the vacuum and the flow distributor, the HPDC samples exhibited a microstructure with substantially high uniformity, i.e., similar to 90% lower porosity and similar to 80% less ESCs than those of conventional HPDC samples. Tensile and fatigue tests showed that the initiation of the crack, i.e., the primary mechanism determining the sample failure, was highly sensitive to the shrinkage pores connected with gas pores and the large and complex shrinkage pores induced by ESCs. (C) 2015 Elsevier B.V. All rights reserved.