This thesis investigated the effect of nickel as an alloying element on the morphology and mechanical values, in particular on the high-temperature strength of aluminum alloys. For this purpose, two test series of common alloys with increasing nickel content were produced. One series of tests covers the range of the commonly used AlSi7Mg0.3 alloy (EN AC-42100), and a piston alloy AlSi12Mg1Cu1 (EN AC-48000) was chosen specifically for the range of high-temperature aluminum alloys. For each series of experiments, three melts were prepared and the nickel content was increased by 0.5% in each case, starting with nickel-free melts. To determine the mechanical properties, the cast specimens were tested by tensile testing at room temperature and 180°C after T6 heat treatment. The effect of nickel on the grain size or solidification properties, as well as the microstructure, was performed using an optical microscope. The distribution of precipitates and formed phases could be analyzed in the scanning electron microscope by EDX mapping.
The addition of nickel to aluminum alloys generally leads to an increase in strength, as well as specifically to high-temperature strength. The high-temperature tensile strength of the AlSi7Mg0.3 alloy was increased from 233 MPa to 254 MPa, which corresponds to an improvement of about 10%, by adding 1% nickel. With the AlSi12Mg1Cu1 alloy, at least a lower increase of 3% to 302 MPa could be achieved. However, this improvement is accompanied by a decrease in elongation at break and a slight increase in grain size. Microstructural investigations using a scanning electron microscope allowed the detection of Al3Ni phases in the edge region between eutectic silicon and the α-matrix. By incorporating these hard phases, as well as other thermally stable aluminides, the mechanical properties can be increased depending on their size and volume fraction.