The project is a continuation and reporting of 3 year G projects in high performance Al alloys, HPAL.
The work has focused on gaining knowledge especially in two areas; how to increase the strength and toughness of commercial Al-Si alloys at elevated temperatures and at room temperature. A literature study has shown how to achieve very good properties through the addition of various alloy additions and the use of customized alloys. In this project the starting point has been
conventional alloys, and better properties would be achieved both by optimizing alloying elements and by minimizing defect levels with improved gating system.
A new test specimen model was designed in CAD. To show the influence of the melt flow on defects, and hence strength, the model was made in two versions; good resp. less good injection system. Sand moulds were produced using a 3D sand printer. The results of the tensile test became unexpected; the difference between the groups was very small.
In the work of alloy with improved ductility, an alloy from the literature was chosen, using Cr to partially replace Mg. As starting alloy, AlSi7Mg was selected. Test specimens were produced in a gradient furnace, where a controlled solidification helps to minimize defects. The result shows that the Cr addition gave a slight increase in toughness, but after conventional aging, a severe reduction in strength was achieved. Aging at longer times gave strength comparable to the basic alloy without Cr, but lower than the alloy from literature.
Directional solidification trials has illustated the importance of silicon as an alloying element on the mechanical properties at elevated temperature (230 C) for an Al-Si9-Cu3-Fe-alloy. An increase of silicon from 9,1 to 12,4 % improves the mechanical properties at room temperature as well as at elevated temperatures. Compared to the base-alloy EN AC 46000 (STENAL 460) the increase in yield strength, ultimate tensile strength and fracture elongation was 49, 17 and 20 % respectively at 230 C. The corresponding increase at room temperature was 16, 22 and 69 % respectively. A Master Thesis work at Jönköping University demonstrate the influnce of silicon, cobolt and nickel on the elevated temperature mechanical properties for Al-Si-alloys.