Homogeneity of die castings is influenced by wide range of technological parameters as piston velocity in filling chamber of die casting machine, filling time of mould cavity, temperature of cast alloy, temperature of the mould, temperature of filling chamber, surface pressure on alloy during mould filling, final pressure and others. Based on stated parameters it is clear, that main parameters of die casting are filling time of die mould cavity and velocity of the melt in the ingates. Filling time must ensure the complete filling of the mould cavity before solidification process can negatively influence it. Among technological parameters also belong the returning material, which ratio in charge must be constrained according to requirement on final homogeneity of die castings. With the ratio of returning material influenced are the mechanical properties of castings, inner homogeneity and chemical composition.

The technology of high-pressure die-casting (HPDC) of aluminum alloys is one of the most used and most economical technology for mass production of castings. High-pressure die-casting technology is characterized by the production of complex, thin-walled and dimensionally accurate castings. An important role is placed on the effective reduction of costs in the production process, wherein the combination with the technology of high-pressure die-casting is the possibility of recycling using returnable material. The experimental part of the paper focuses on the analysis of a gradual increase of the returnable material amount in combination with a commercial purity alloy for the production of high-pressure die-castings. The returnable material consisted of the so-called foundry waste (defective castings, venting and gating systems, etc.). The first step of the experimental castings evaluation consisted of numerical simulations, performed to determine the points of the casting, where porosity occurs. In the next step, the evaluation of areal porosity and microstructural analysis was performed on experimental castings with different amounts of returnable material in the batch. The evaluation of the area porosity showed only a small effect of the increased amount of the returnable material in the batch, where the worst results were obtained by the casting of the alloy with 90% but also with 55% of the returnable material in the batch. The microstructure analysis showed that the increase in returnable material in the batch was visibly manifested only by a change in the morphology of the eutectic Si.

At present, Al-Si-Cu based alloys (with a typical representative AlSi9Cu3 alloy) represent more than half of the castings used in various industries (automotive, aerospace and electrical engineering). These are most often sub-eutectic (exceptionally eutectic) alloys with a content of 6 to 13 wt. % Si and 1 to 5 wt. % Cu. The aim of the paper is to point out the importance of the evaluation of input raw materials that determines the overall properties of the casting and the costs invested in its production. A negative impact on performance can be expected when using an alloy made up of a high proportion of recycled material, despite its economic benefits. Experimental alloys were evaluated based on the results of crystallization process and a combination of scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and deep etching. The effect of remelting and increasing the remelted returnable material in the batch was manifested especially in the crystallization of iron-rich phases. The negative effect of remelting on the structural components was manifested after the fourth remelting. Gradual increase of remelted returnable material in the batch causes harmful changes in the crystallization process.