Thermo fatigue cracking of die casting dies

The investigation of aluminium alloy die casting die failures was done with the emphasis on thermal cracks. The aim of the study was to prolog the in-service die life by cladding with maraging steels, which would be economically beneficial. A vast analysis of thermal fatigue cracks in aluminium alloy die casting is done. Immersion test apparatus was developed, which enables simulation of conditions during aluminium alloy die casting and enables controlled thermal fatigue testing of materials. Special specimens made of the AISI H13 tool steel were differently heat treated. On the edges of some specimens, the maraging steel is cladded using gas tungsten arc (GTA) welding. These samples are tested in as-welded and in optimally aged condition. After completion of a particular number of cycles, the specimen edge surfaces were examined visually. The specimens were then sectioned and examined with light and scanning electron microscopy (SEM). The energy-dispersive X-ray spectroscopy (EDS) mapping of areas around the cracks was done. The number and length of thermal fatigue cracks were statistically evaluated and a Vickers hardness profiles were measured. The results confirmed a good thermal fatigue resistance of the properly hardened H13 hot work tool steel. The surface cracks growth is accelerated by surface oxidation.

► An immersion test machine was developed for simulation of thermal fatigue testing.
► A thermal fatigue resistance of tool steel and welded maraging steel was tested.
► A FEM was developed for prediction of stresses and optimization of test specimen.
► A phenomenon of thermal cracking of die casting dies is explained in detail.
► Crack growth promoted by changes in chemical composition (oxidation) is explained.