Bestimmung der Lastverteilung in Al-Si Legierungen mittels in-situ Synchrotron Diffraktometrie

Abstract

Cast Al-Si alloys are part of our everyday lives and used for many automotive components such as cylinder heads, pistons and valve lifters. For piston alloys high temperature strength is an important requirement, because the temperature at the surface of a combustion chamber can reach up to 400°C.<br />Load transfer from Al to Si and intermetallic phases contributes to RT and hightemperature strength of cast Al-Si alloys. The eutectic silicon forms long range three dimensional structures of interconnected lamella with large aspect ratios that disintegrate during heat treatment at temperatures close to the eutectic point. Isolated rounded particles of silicon develop within the alloy and, as a result, the strength decreases. Also, Cu-, Ni-, and Fe-rich aluminides form similar networks and, in addition, hinder the spheroidisation of the eutectic Si. This interconnected network of aluminides and Si increases the strength of these alloys compared to AlSi12. In this work, the load partition between phases during compression tests at room temperature and 300°C is investigated by in-situ synchrotron diffraction for an AlSi12 cast alloy and an AlSi10Cu6Ni2 piston alloy. The alloys are studied in as cast condition and after solution heat treatment at 500°C for 1h and 4h.<br />For the in-situ compression tests, the high flux and brilliance of synchrotron radiation offers the possibility of short acquisition time and therefore allows following the evolution of the load partition between phases in-situ during deformation. The silicon phase in AlSi10Cu6Ni2 experiences 60% more interplanar strain than the same phase in AlSi12 and the decrease in its load carrying capacity by solution heat treatment is ~ 10% for 300°C. The evolution of the microstructure during deformation shows that the formation of subgrains in the Al-matrix with a preferred texture for the AlSi12 alloy.