Although rheocasting is widely used for the production of thin-walled components, thick-walled rheocast components are not yet common. In this paper, thick-walled semi-solid cast components were manufactured using serial production equipment. The aim of the investigation was to replace components made of spheroidal graphite cast iron (SGI) and conventionally cast aluminium in order to lower the weight of the truck, and still fulfill the high demands set on serial production. The rheocasting process used was a modified Rapid-S process coupled with a TX630 aluminium alloy and T5 or T7 heat treatment. Two different serial production rheocast components were fatigue tested by means of constant amplitude rig testing in order to define Wöhler curves. Moreover, multi-axial shake testing with signals recorded from proving ground was carried out. Fracture surfaces as well as metallographic samples were investigated.
Fatigue properties of two kinds of ferrous powder metals, which were produced from partially prealloyed iron powders and whose densities are 7.10g/cm3 and 7.35g/cm3, were investigated by tension-compression fatigue test.Main fatigue cracks did not initiate from pores but from slip bands in soft Fe particles in both these materials. The crack nucleated at the maximum Fe particle behaved as a defect larger than the maximum pore and accordingly the maximum size of the Fe particle existing on specimen surface was the crucial factor determining the fatigue strength. In order to confirm this fact more exactly, the maximum Fe particle size was evaluated by the statistics of extremes, and on the other hand an artificial hole with various sizes was introduced onto the specimen surface and the influence of the hole was investigated. The prediction of the maximum size of Fe particle by the statistics of extremes was in good agreement with the critical size of the artificial hole which was detrimental to fatigue strength.These facts explain that the difference in the fatigue strength between two materials was not caused by the difference in densities, i.e. pores, but by the strength properties of the microstructures such as Vickers hardness which was measured in details from the core to boundaries of grains.
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