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Effect of chemical composition variation on mechanical properties of 6xxx aluminum alloys

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The 6xxx-group contains magnesium and silicon as major addition elements. These multiphase alloys belong to the group of commercial aluminum alloys, in which relative volume, chemical composition and morphology of structural constituents exert significant influence on their useful properties [1÷4]. In the technical 6xxx aluminium alloys contents of Si and Mg are in the range of 0.5÷1.2 wt. %, usually with a Si/Mg ratio larger than one. Besides the intentional additions, transition metals such as Fe and Mn are always present. If Si content in Al alloys exceed the amount that is necessary to form Mg2Si phase, the remaining Si is present in other phases, such as Al-Fe-Si and Al-Fe-Si-Mn particles [1, 5÷13]. The aluminium alloys of 6xxx group have been studied extensively because of their technological importance and their exceptional increase in strength obtained by precipitation hardening. The 6xxx aluminium alloys are mostly used in extruded products, as well as for construction and automotive purposes. The ease with which these alloys can be shaped, their low density, their very good corrosion and surface properties and good weldability are factors that together with a low price these make them commercially very attractive. The precipitation of the metastable precursors of the equilibrium β(Mg2Si) phase occurs in one or more sequences which are quite complex. The precipitation sequence for 6xxx alloys, which is generally accepted in the literature [1, 7], is: SSSS → atomic clusters →GP zones → β″→ βʹ→ β (stable) Some authors [8] consider the GP zones as GP1 zones while the β″ is called a GP2 zone. The most effective hardening phase for this types of materials is β″. The medium strength AlMgSi aluminium alloys are commonly processed by extrusion. Their extradubility depends to a large extent on chemical composition, casting condition and heat tre[...]

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