Magnesium alloys are one of the lightest of all the structural materials. Because of their excellent physical and mechanical properties the

alloys have been used more and more often in various branches of industry. They are cast mainly (over 90%) on cold and hot chamber die

casting machines. One of the byproducts of casting processes is process scrap which amounts to about 40 to 60% of the total weight of a

casting. The process scrap incorporates all the elements of gating systems and fault castings. Proper management of the process scrap is

one of the necessities in term of economic and environmental aspects.

Most foundries use the process scrap, which involves adding it to a melting furnace, in a haphazard way, without any control of its content

in the melt. It can lead to many disadvantageous effects, e.g. the formation of a hard buildup at the bottom of the crucible, which in time

makes casting impossible due to the loss of the alloy rheological properties. The research was undertaken to determine the effect of an

addition of the process scrap on the mechanical properties of AZ91 and AM50 alloys. It has been ascertained that the addition of a specific

amount of process scrap to the melt increases the mechanical properties of the elements cast from AZ91 and AM50 alloys.

The increase in the mechanical properties is caused mainly by compounds which can work as nuclei of crystallization and are introduced

into the scrap from lubricants and anti-adhesive agents. Furthermore carbon, which was detected in the process scrap by means of SEM

examination, is a potent grain modifier in Mg alloys [1-3].

The optimal addition of the process scrap to the melt was determined based on the statistical analysis of the results of studies of the effect

of different process scrap additions on the mean grain size and mechanical properties of the cast parts.

The aim of the study was to select the optimal content of zirconium introduced as an alloying additive to obtain the best strength properties of Al-Si alloy. A technically important disadvantage is the tendency of silumins to form a coarse-grained structure that adversely affects the mechanical properties of castings. To improve the structure, modification processes and alloying additives are used, both of which can effectively refine the structure and thus increase the mechanical properties. According to the Hall-Petch relationship, the finer is the structure, the higher are the mechanical properties of the alloy. The proposed addition of zirconium as an alloying element has a beneficial effect on the structure and properties of silumins, inhibiting the grain growth. The starting material was an aluminium-silicon casting alloy designated as EN AC-AlSi9Mg (AK9). Zirconium (Zr) was added to the alloy in an amount of 0.1%, 0.2%, 0.3%, 0.4% and 0.5% by weight. From the modified alloy, after verification of the chemical composition, samples were cast into sand moulds based on a phenolic resin.
The first step in the research was testing the casting properties of alloys with the addition of Zr (castability, density, porosity). In the next step, the effect of zirconium addition on the structure and mechanical properties of castings was determined.