Effect of scrap on the microstructure and mechanical properties of en AB-42000 alloy pressure die castings

Shrinking resources of primary raw materials, as well as environmental and economic considerations, are prompting casting manufacturers to use a higher proportion of process secondary aluminum. This also applies to aluminum alloys, from which the resulting castings should be made with at least 60-80% secondary material content. Unfortunately, this process results in an increased proportion of various impurities (metallic and gaseous), with iron being one of the most important. Depending on the crystallization conditions, chemical composition and technology for obtaining aluminum alloys, it can be a component of eutectics and exist in the form of many intermetallic phases with different stoichiometric compositions, with Al5FeSi as one of the worst. This phase, in the poured state, crystallizes in a lamellar form (on the surface of acicular microstructure), with sharp edges and "pointed"corners, causing stress concentration and propagation of micro-cracks. This causes brittleness of castings, makes machining more difficult and reduces their mechanical properties, which are often a marketability criterion. The article includes a study of the effect of process scrap/secondary aluminum, and therefore increasing iron content, on hardness HB and mechanical properties (UTS; YS; A) of EN AB-42000 (AlSi7Mg) alloy from which car rims are low-pressure die cast.