Dependence of mechanical properties on porosity of AlSi7Mg0.3 alloy during gravity casting
2019
Hren, I., Jan Evangelista Purkyne Univ. in Usti nad Labem (Czech Republic) | Michna, S., Jan Evangelista Purkyne Univ. in Usti nad Labem (Czech Republic) | Michnova, L., Jan Evangelista Purkyne Univ. in Usti nad Labem (Czech Republic)
In cast material, due to the technology and process used, the presence of defects in the cast material structure, such as porosity, inclusions and oxidative membranes, is inevitable. All these discrepancies have a negative effect on the resulting mechanical value of the cast material. Several works have shown that especially porosity in particular negatively degrades the fatigue properties, strength and ductility of the material. Since most fatigue failures begin at the surface of the material, surface roughness becomes an extremely important factor in determining the fatigue strength of the cast parts, and structural defects (porosity, inclusions, oxide membranes) near the surface have a decisive influence on the initiation of material breakage. The work is focused on the fractographic analysis of the fracture surface of AlSi7Mg0.3 casting alloy. Using the electron scanning microscope, the fracture area of the samples was analysed. Optical metallography identified structural components of castings just below the fracture surface as well as the course of the fracture line. An increased number of oxygen, carbon, chlorine and fluorine elements occurred on the surface of the samples. The occurrence of these elements most likely results in material breakage, which also confirms the results achieved by the static tensile test. On the basis of the obtained results from the performed analyses, mechanisms of breaking of alloyed material of Al-Si type alloys were determined.
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