Analysis of the defects occurrence on the functional surfaces of individual mould segments for the tyre production from AlSi7Mg0.3Sr

Abstract

The basic prerequisite for obtaining a quality casting according to the requirements and specifics of the customer is the production of the mould (in our case using low-pressure die-casting) without the occurrence of surface defects in the form of cracks, scabs, microshrinkages and local depressions. In this case, the mould segments for the tyre production are those which show tiny cracks or scabs on the functional surface of the castings that define the surface quality of the resulting product. It is necessary to analyse these defects in order to eliminate the causes of their formation in the casting process. For this reason, a new alloy of eutectic silumin AlSi9 alloyed with Mg, Mn and modified Sr was prepared in order to improve the fluidity and maintain the mechanical properties of the material up to 250 ℃ The subject of the study was the analysis of the surface defects of the mould, including the analysis of the chemical composition (energy-dispersive X-ray) and microstructure in the defect area. In order to investigate the subsurface layer of defects, metallographic specimens of cross-sections were prepared by means of mould, which were examined by light and electron microscopy. The detailed microstructural characterization of individual elements was performed on lamellas of the mould studied using transmission electron microscopy. An X-ray diffraction analysis was performed to investigate the residual stress at the defects area very closely. It has been found that a smaller number of defects on the functional surfaces can be obtained by changing the mould position during casting.