Aluminium alloy with increased resistance and low quench sensitivity

Abstract

An aluminium alloy having high mechanical strength and low quench sensitivity comprising 4.6 to 5.2 wt. % Zn, 2.6 to 3.0 wt. % Mg, 0.1 to 0.2 wt. % Cu, 0.05 to 0.2 wt. % Zr, max. 0.05 wt. % Mn, max. 0.05 wt. % Cr, max. 0.15 wt. % Fe, max. 0.15 wt. % Si, max. 0.10 wt. % Ti and aluminium as the remainder along with production related impurities, individually max. 0.05 wt. %, in total max. 0.15 wt. %. A process for producing plates having a thickness of more than 300 mm for manufacturing moulds for injection-moulding plastics is made up of the following steps: continuous casting the alloy into ingots having a thickness greater than 300 mm, heating the ingots to a temperature of 470 to 490° C. with a max. heating rate of 20° C. / h between 170 and 410° C., homogenising the ingots for 10 to 14 h at a temperature of 470 to 490° C., cooling the ingots in still air to an intermediate temperature of 400-410° C., cooling the ingots by means of forced air cooling from the intermediate temperature of 400-410° C. to a temperature of less than 100° C., cooling the ingots to room temperature, artificially age-hardening the ingots at elevated temperature. The artificially age-hardened ingots can be employed for manu-facturing moulds for injection-moulding plastics.

Description

BACKGROUND OF THE INVENTION [0001] The present invention relates to an aluminium alloy having high strength and low quench sensitivity. Also within the scope of the invention is a process for manufacturing thick plates of the aluminium alloy. [0002] In particular in the automobile industry there is an increasing demand for large plastic components such as e.g. integral bumpers. In order to manufacture the corresponding large moulds for injection moulding purposes it is necessary to have plates with a thickness often greater than 150 mm, in some cases even greater than 500 mm. [0003] Today, normally hot rolled and artificially aged, i.e. plates heat-treated at elevated temperature, are employed for manufacturing injection moulding moulds with a thickness e.g. of 50 to 300 mm. Larger moulds, thicker than 300 mm, are manufactured either out of forged blocks or directly from continuously cast ingots. [0004] One significant disadvantage of the aluminium alloys employed today for mould ma...

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Benefits of technology

[0006] A further objective of the invention is to provide a suitable process by means of which the al...

Problems solved by technology

One significant disadvantage of the aluminium alloys employed today for mould manufacture is their high quench sensitivity.

Due to the resultant high temperature gradients between the surface and the core of the ingot or plate, the magnitude of the undesirable internal stresses increases, so that also for this reason there are limits to increasing the cooling rate further and with that the strength level that can be reached.

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