Although the market for cylinder heads will diminish in the future, there still is a big demand for materials with a low density and good mechanical properties at elevated temperatures especially for electric driven vehicles. Aluminium-manganese casting alloys usually contain no more than 1.6 wt.-% Mn. In our group, we are developing a hypereutectic and therefor unusual alloy with up to 4 wt.-% Mn. This alloy type provides good combination of high heat resistance, high thermal conductivity and moderate strength while keeping its properties during long-term exposure at temperature making it ideal for applications like housings of e-drives or thermal management of batteries. Since in this type of alloy primary phase crystallize as coarse, faceted intermetallic Al₆Mn-particles measures has to be taken, to transfer them into a fine dispersion of small particles. Since the gravity die casting process predefines cooling velocity, achievable undercooling is somehow limited, but there are other metallurgical methods to reach the target:

1) Enhanced heterogeneous nucleation by intentional addition of potential nucleation sites.

2) Avoiding heterogeneous nucleation by removing potential nucleation sites already present in the melt thus increasing undercooling.

3) Inhibition of nucleus growths by poisoning or induced twinning by adding surface-active alloying / trace elements.

For the determination of the suitable grain refiners, Al₆Mn primary particles were extracted by chemical phase isolation from various experimental alloys. By measuring their lattice constant, we gained information about potential nucleating agents. Several substances were then tested to receive a marked reduction in particle size. Presumably surface-active alloying elements in various concentrations were tried out, to shift the faceted type of primary solidification to non-faceted type with a much smoother - on a microscopically scale - interface morphology. Casting trial were made to obtain tensile and hardness samples. Long-term exposure trials were conducted up to 450 °C for 500 and 1000 h, respectively, to characterize the degradation of the different experimental alloys. This paper gives a first overview over the results obtain so far.