A high strength cast aluminum alloy with accelerated response to heat treatment

Abstract

The invention relates to an improved cast Al alloy designed to provide an accelerated response to heat treatment; specifically, the alloy's response to thermal growth during aging is accelerated, leading to a dimensionally more stable casting. This improvement is achieved by the addition of trace amounts of Sn, In, Ge or Cd to an Al-Si-Cu cast alloy. The improved alloy has particular application for cast Al engine blocks and cylinder heads.

Description

[0001] This application claims the benefit of U.S. provisional application Ser. No. 60 / 320,143 filed Apr. 24, 2003.BACKGROUND OF INVENTION[0002] 1. Field of the Invention[0003] The field of this invention relates to cast aluminum alloys having an accelerated response to heat treatment and a method for the same.[0004] 2. Background Art[0005] Cast aluminum engine blocks and cylinder heads, such as those made from Al--Si--Cu--Mg alloys (e.g., a broad array of the 3xx.x class of alloys), are often heat-treated after casting to impart increased mechanical strength to the alloy via precipitation hardening. The heat treatment process usually comprises a solution treatment stage, a quenching stage, and an aging stage. During the solution treatment stage, the alloy is heated above its solubility limit to homogenize the alloy. The length of time that the alloy is heated above its solubility limit is often dictated by the amount of inhomogeneity in the alloy before heat treatment. During the q...

AI Technical Summary

Benefits of technology

[0011] The present invention relates to a new alloy that provides improved heat treatment response and thus decreased aging times for engine blocks and heads, which results in significant savings of costs associated with heat treatment. This new alloy also results in decreased variability in its response to heat treatment. More specifically, under this invention, a multi-component alloy, such as the aluminum-silicon-copper-magnesium (Al--Si--Cu--Mg) alloys currently used for engine blocks and heads, is improved so that the alloy includes trace additions of tin. The inclusion of trace amounts of Sn, up to 0.1 wt. % Sn, have a significant effect on the thermal growth kinetics and thus on the heat treatment response of cast aluminum alloys. The use of Sn at relatively low levels, from 0.01 to 0.1 wt. %, can result in as much as a 50% increase in kinetic response to heat treatment, compared with a similar alloy containing less than 0.01% Sn.

[0012] Accordingly, this invention provides a new, refined alloy chemistry obtained by narrowing the currently acceptable range of Sn levels in engine block and head alloys. With this new alloy composition, one can simultaneously produce an alloy which results in a cost savings, due to improved heat treatment response and thus decreased aging times, and also decreased variability in its response to heat treatment. It is further believed that trace additions, in the range of 0.01 to 0.1 wt. %, of In, Cd and Ge also provide the requisite improved response to aging.

[0023] The prior art further suggested that the Sn, In, and Cd additions enhanced the nucleation of Al.sub.2Cu .theta.' precipitates. The prior art showed that the additions of Sn, In and Cd caused an increase in .theta.' precipitates, and that simultaneously a decrease in GP zones, thus explaining the diminished hardness during natural aging, where GP zones typically predominate, and the enhanced effect during artificial aging, where .theta.' is present. As a result, the prior art advocated Al--Cu alloys including Sn in an amount between approximately 0.03 and 0.05 wt. %.

Problems solved by technology

This new alloy also results in decreased variability in its response to heat treatment.

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