The ratio of primary and secondary alloy in the batch is important in determining and evaluating the quality of the alloy. The resulting quality of the casting and the costs associated with its production are directly related to the composition of the raw materials entering the smelting process. With the use of an alloy composed of a high proportion of recycled material a negative effect on performance can be expected despite its economic benefits. Based on the results of thermal analysis, mechanical properties and microstructure analysis, the effect of changing the primary and secondary AlSi9Cu3 alloy ratio in the batch was determined. A negative effect of the increasing proportion of secondary alloy was already evident in the case of an alloy composed of a 50-50% ratio. Conversely, in the case of artificial aging, a positive effect was observed with increasing amounts of secondary alloy.

The aim of the paper is to describe and specify the properties and microstructure of Al-Si alloy using Zr, a combination of Zr with elements used in the grafting of Al (Ti) alloys, and modification (Sr). Al-Si alloys with a combination of Zr and Ti and Sr elements represent an opportunity for the development of new aluminum alloys with a specific use. The experiment focused on the analysis of the synergistic effects of Zr with Ti and Zr with Sr on a AlSi7Mg0.3Cu0.5 alloy. The experimental alloys contained a constant Zr content of 0.15 wt. % and were alloyed with a gradual addition of Ti and Sr in the range of 0.1 to 0.3 wt. % for Ti, and 0.1 to 0.3 wt. % for Sr. The experimental samples were cast by meltable model casting technology. In variants with a constant addition of Zr 0.15 wt. % and a gradual addition of Ti, we observed an increase in the values of mechanical characteristics, with a significant decrease in ductility. When evaluating the structure of experimental alloys, Ti affected it by increasing the number of precipitated Zr phases. Experimental alloys with Zr and Sr addition were characterized by nucleation of Zr phases in angular morphology. It can be concluded that the investigated elements are expected to have a positive (strengthening) effect even at higher operating temperatures.

The main objective of this paper is to investigate the effect of Zr and its synergistic effect together with the addition of an inoculant (Ti) and a modifier (Sr) in terms of structural analysis and mechanical characteristics of AlSi7Mg0.3Cu0.5 alloy. In accordance with the objectives of the paper, in the experimental part, eight material variants were cast by the investment casting method. The presence of Zr in the experimental alloys was manifested by the crystallization of phases with different chemical compositions mainly (AlSi)3(TiZr) and (AlSi)2(TiZr). The graded addition of Ti in the alloys resulted in a higher number of nucleation grains of Zr-rich phases, and alloys with a combination of Zr and Sr were characterized by the formation of (AlSi)2(TiZr) phases. Various types of precipitates based on Zr (Al3(ZrTi)) and Cu (Al2Cu) were observed in the substructure of the alloys. The addition of Zr and its synergistic effect with Ti and Sr led to an increase in the conventional yield strength, hardness and partly tensile strength with reduced elongation of the experimental alloys.

The main reason for the use of returnable material, or recycled alloys, is a cost reduction while maintaining the final properties of the casting. The casting resulting quality is directly related to the correct ratio of commercial grade alloy and alloy made by remelting the returnable material in the batch. The casting quality is also affected by the purity of the secondary raw materials used, the shape complexity and the use of the casting itself. The presented article focuses on the effect of increasing the returnable material content in the batch on the hot tearing susceptibility of AlSi9Cu3 alloy. Hot tears are a complex phenomenon that combines metallurgical and thermo-mechanical interactions of the cast metal. Hot tearing susceptibility was evaluated on the basis of quantitative (HTS—hot tearing susceptibility index) and qualitative evaluation. The negative effect of returnable material in the batch was already manifested at a 20% content in the batch. The critical proportion of the returnable alloy in the batch can be stated as 50%. The alloy with a 50% returnable material content manifested insufficient results of the HTS index and qualitative evaluation, which means increased sensitivity to tearing. The negative effect of returnable material and the increased sensitivity were also confirmed in the evaluation of the fracture surface and hot tear profile. The microstructure of alloys with 50% and higher proportion of returnable material was characterized by a higher amount of iron phases (mainly Al5FeSi), whose sharp ends acted as critical regions of hot tearing and subsequent hot tear propagation, which had a major impact on the increase in hot tearing susceptibility.