Simulation-based design of 5xxx series alloys with improved resistivity against intergranular corrosion for automotive applications

摘要

Resistivity against intergranular corrosion (IGC) is one of the major requirements for AlMgMn 5xxx-series alloys for automotive chassis applications. In 5xxx alloys IGC is caused by the formation of β-Al_5Mg_3 precipitates along the grain boundaries. Today's 5xxx alloys for chassis applications have been developed such that under specific test conditions they will not exceed a certain mass loss by IGC. However, current developments in the automotive industry will lead to an increased temperature load on chassis parts, in particular for front axle applications in the vicinity of the car engine. Therefore it is to be expected that the properties of the existing 5xxx series alloys will not be sufficient any more. Certain alloy elements, including Mn, Cr, Cu and Zn, alter type and morphology of the Mg-bearing precipitates and, hence, reduce the sensitivity against IGC. The present study was aimed at developing a series of Zn-containing Al alloys which are free of IGC, while maintaining mechanical properties of current 5xxx chassis alloys. Alloy development was performed by micro-chemistry simulation with the aim to avoid the formation of the detrimental β-Al_5Mg_3 precipitates. Eventually a series of three alloys was cast and processed on lab scale and tested for mechanical properties and resistivity against IGC after application of various critical time/temperature scenarios in order to validate that the newly developed alloys are free of IGC.