Regensburg 2007 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 36: Nano structured materials IV

MM 36.4: Vortrag

Donnerstag, 29. März 2007, 15:30–15:45, H4

Microstructure Analysis of Al-Mg-Si alloys with respect to its influence on strength — •Cynthia Chang, Nelia Wanderka, and John Banhart — Hahn-Meitner-Institut Berlin, Glienicker Str. 100, 14109 Berlin

Al-Mg-Si - based alloys are widely used in automotive industry owing to their high strength, good formability and low density. During paint baking of car bodies at 180°C the metal alloy hardens. The increase of hardness is due to the formation of small needle-like precipitates.

In the present work the influence of different Mg and Si contents is investigated. Alloys with compositions Al-0.4Mg-0.4Si and Al-0.4Mg-1.0Si were characterized after different heat treatments using TEM and microhardness measurements. The strengthening by natural ageing of the both alloys is different. In the case of the Al-0.4Mg-0.4Si alloy the natural aging increases the microhardness after subsequent artificial aging at 180°C, while in case of the Al-0.4Mg-1.0Si alloy it decreases. Preceding natural aging has a positive influence on the strength of Al-0.4Mg-0.4Si and a negative one on Al-0.4Mg-1.0Si alloy.

TEM analysis showed that the small needle-like precipitates of both alloys are oriented parallel to the <001> directions of the Al matrix. While the Al-0.4Mg-0.4Si alloy shows a large number of dislocations beside the needle-like precipitates, no dislocation in the Al-0.4Mg-1.0Si alloy were observed. The number density and the size of needle-like precipitates of both alloys are different too.

The different strengthening behaviour of both materials is discussed with respect to their different microstructure.