Cast Aluminium Alloy

Abstract

Cast aluminium alloys comprising 1.0-8.0% in weight magnesium (Mg), >1.0-4.0% in weight silicon (Si), 0.01-<0.5% in weight scandium (Sc), 0.005-0.2% in weight titanium (Ti), 0-0.5% in weight of at least one element or selected from the group consisting of zirconium (Zr), hafnium (Hf), molybdenum (Mo), terbium (Tb), niobium (Nb), gadolinium (Gd), erbium (Er) and vanadium (V), 0-0.8% in weight manganese (Mn), 0-0.3% in weight chromium (Cr), 0-1.0% in weight copper (Cu), 0-0.1% in weight zinc (Zn), 0-0.6% in weight iron (Fe), 0-0.004% in weight beryllium (Be), and the remainder of aluminium with further impurities to an individual maximum of 0.1% in weight and totally maximally 0.5% in weight.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application is a 371(c) National Stage of PCT / DE2004 / 002425 filed Nov. 3, 2004, which claims priority to Germany patent application Serial No. 103 52 932.2 filed Nov. 11, 2003, the disclosures of which are incorporated herein in their entireties.FIELD OF THE INVENTION [0002] The present invention relates to a cast aluminium alloy suitable particularly for thermally highly stressed cast parts. By using the cast aluminium alloy according to the invention, the efficiency of cast parts produced therefrom is improved considerably, their thermal stability being guaranteed up to temperatures of 400° C. BACKGROUND OF THE INVENTION [0003] By means of modern casting methods, such as the diecasting method, the sand casting method, the permanent-mold casting method or the thixocasting and rheocasting method, which are very far developed technically, highly stressable cast parts can currently be produced from aluminium alloys. [0004] By means o...

AI Technical Summary

Benefits of technology

[0029] The addition of scandium is essential. In addition to an intensive particle hardening, the scandium causes a grain refining of the cast structure and a recrystallization inhibition as a result of the thermally very stable Al3Sc particles. Cast parts produced from the alloy according to the invention, therefore have the advantage that their mechanical characteristics are stable up to temperatures of 400° C. The cast alloy according to the invention is therefore predestined mainly for thermally highly stressed cast parts. It is also advantageous, that, as a result of the high thermal stability, a replacement of aluminium materials by materials of a high density is not required. By the use of the alloy according to the invention, the component weight is guaranteed while the conductivity is increased, which component weight can even be reduced by cast parts which have thinner walls. It is another advantage that the weldability is also improved by means of the scandium fraction. The scandium content is preferably between 0.01-0.45% in weight, particularly preferably between 0.015-0.4% in weight.

[0030] Like scandium, titanium also causes a grain refining and therefore contributes in a corresponding manner to the improvement of the thermal stability. In addition, titanium lowers the electric conductivity. The titanium content preferably amounts to between 0.01-0.2% in weight, particularly between 0.05-0.15% in weight.

[0031] Since zirconium has the same effect as scandium or titanium, it is also advantageous to additionally admix zirconium to the alloy. The effect of the scandium of causing an intensive particle hardening by the thermally very stable Al3Sc particles, a grain refining of the structure as well as a recrystallization inhibition is further increased by the combined effect of scandium and zirconium. Zirconium substitutes Sc atoms and forms particles of the ternary compound Al3(Sc1-xZrx) which have less of a tendency to coagulate at higher temperatures than the Al3Sc particles. The scandium and zirconium constituents again improve the thermal stability of the alloy in comparison to an alloy which contains only scandium. This permits a further optimization in the direction of lower scandium contents for lowering the cost. The zirconium content of preferred embodiments is between 0.01-0.3% in weight or 0.05-0.1% in weight.

[0032] In addition to the increase of thermal stability by adding scandium, titanium and possibly zirconium, there is the advantage that the cast aluminium alloy already has the thermal-stability-increasing effect as cast. As a result of the subsequent heat treatment in a temperature range of typically 250-400° C., the mechanical characteristics with the corresponding thermal stability are finally achieved. By means of the appropriate selection of the temperature and the time duration-as known, the time duration depending on the component size and thickness-the thermal stability can be varied correspondingly. A solution heat treatment with a subsequent artificial aging is not required, which is advantageous in that the problem concerning the distortion will not play any role, which distortion usually requires a measuring and aligning and, as known, occurs in the case of classical solution-heat-treated and artificially aged cast aluminium alloys.

[0034] However, it is particularly advantageous for the alloy to contain at least 0.001% in weight, preferably at least 0.008% in weight vanadium. Vanadium acts as a grain refiner, similarly to titanium. Furthermore, it improves the weldability and reduces the scratching tendency of the molten material.

Problems solved by technology

These alloys are not suitable for thermal stresses of up to 400° C. The classical cast aluminium alloys are thermally stable only up to approximately 200° C.

It is a disadvantage that a distortion occurs as a rule during the solution heat treatment, which distortion has to be corrected by additional measures or operating steps (measuring and aligning).