Effect of vacuum on porosity and mechanical properties of high-pressure die-cast pure copper

Pure copper tensile bars were produced by conventional die casting (HPDC) and vacuum-assist die casting (VADC) processes. Porosity and mechanical properties were investigated by using optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray computed tomography (XCT) and tensile tester. Results show that porosities including gas porosity and shrinkage porosity could be observed in copper castings. Since the application of vacuum could reduce filling related gas entrapment and facilitate solidification due to the increased heat transfer between metal and die, both number and size of the entrapped gases, as well as shrinkage porosities were significantly reduced in vacuum-assist die castings of pure copper. The porosity fraction decreased from 2.243% to 0.875% compared with that of the conventional die casting. Besides, mechanical properties were improved significantly, i.e., by 15% for ultimate tensile strength and three times for elongation.