An Electronic Approach to the Prediction of the Mechanical Properties of Aluminium Alloys and its Application to the Design of High Strength Alloys

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A quantitative method for predicting the mechanical properties of aluminium alloys was proposed on the basis of the molecular orbital calculation of electronic structures. A new parameter which is the s-orbital energy level, Mk, of alloying elements in aluminium was introduced into this method. The compositional average of this parameter varied linearly with the yield strength and the tensile strength of commercially available wrought aluminium alloys with multiple components. Both the strain hardening and the precipitation hardening of the alloys were also treated well in terms of this parameter alone.Furthermore, in order to understand stress corrosion cracking (SCC), local distributions of Mg atoms were investigated experimentally in Al-Mg based alloys. There was a deficient Mg region in the vicinity of beta precipitates in the grain-boundaries of these alloys. This is probably attributable to the occurrence of SCC in them because of the very weak yield strength of this region in the SCC circumstance. In addition, it was shown from the molecular orbital calculations that there is the possibility of improving the SCC resistance by the addition of Cr, Ti and Nb into aluminium alloys. Finally, employing these results several high strength aluminium alloys were designed successfully.