Effects Of Hot Isostatic Pressing On Microstructure And Properties Of 354-T6 Cast Aluminium Compressor Wheel

Aluminium alloy has become the important lightweight material of automotive industrybecause of its low density, good plasticity and high strength ratio. Nowadays the 354 castaluminium alloy is used as the compressor wheel material of the turbocharger. Thecompressor wheel plays a key role in the function of the turbocharger. With the developmentof the automotive industry, especially for the turbocharger impeller performance expectationscontinue to increase, how to enhance the property of cast aluminium alloy based on currentcasting process is of great significances and became the work orientations of researchers.In this thesis, two batches of 354 aluminium compressor wheel castings, which includeHIPed and non-HIPed castings, were studied. All the test specimens were samplinged fromcastings and then prepared for further investigations. The analysis methods of metallography,tensile test, fatigue test and fractography were used. The comparison and study onmicrostructure and property after HIP process were mainly summarized. The results had beenobtained as follows:After HIP process, the shrinkage porosities can be removed from castings effectively,especially at the thin location (e.g. blade). But very few large-sized shrinkage porosities stillcan not be eliminated absolutely. The microstructure was unaffected.After HIP process, the mechanical properties at room temperature have slightlyimprovements. The data analysis of two-batch samples showed the deviations of HIPedsamples greatly reduced compared with non-HIPed samples, which would improve thereliability of products. The fracture surface of tensile test specimens all showed typicalductile fracture characteristics by scanning electron microscopy.After HIP process, the fatigue property was effectively enhanced. The average fatiguelife of HIPed samples had 2 times more than non-HIPed samples. The fractography on fatiguetested samples also confirmed that the HIPed samples had better resistances to the fatigue-crack initiation by eliminating shrinkage porosities, which have great effects onfatigue life improvement.