Papers by Author: Joseph Langlais

Abstract: The mechanical properties of 206 alloys are among the highest of aluminum alloys. However, these alloys are usually prone to hot tearing. It is known that the addition of silicon can reduce the hot tearing propensity and improve fluidity. However, the commercial 206 alloys used in conventional casting processes limit the silicon concentration ≤0.05 wt% to obtain good mechanical properties. However, the semi-solid forming offers a unique opportunity to increase the silicon content to improve the castability without compromise on mechanical properties. In the present paper, the development of modified 206 alloy compositions to minimize hot tearing during semi-solid forming while maintaining competitive mechanical properties is reported. The effect of high silicon contents with varying copper levels on hot tearing sensitivity is studied. The mechanical properties of a high Si 206 alloy with lowest hot tearing sensitivity are evaluated. It is found that increasing the silicon content in 206 alloys is beneficial to reduce hot tearing. The high Si 206 variants produced by the SEED rheocating process not only reduce significantly the hot tearing sensitivity but also attain superior mechanical properties.

Abstract: The semi-solid forming (SSF) of aluminum alloys offers many advantages over conventional casting processes. Nevertheless, the semi-solid forming is still far from its full commercial potential and mainly used in specific niche markets. The market positioning requires simple, low cost, and versatile SSF processes that are capable of processing a wide range of alloy composition including wrought alloy compositions. However, wrought alloys must be adapted to obtain the desired semi-solid processing ability and proper mechanical properties. The processing of these attractive alloys with the SEED process offers the possibility to better target specific applications and customers’ needs. In the present paper, the alloy development of AA-6061 aiming to minimize the hot tearing propensity during forming process is reported. An overview of the industrial SEED process used to produce the semi-solid AA-6061 feedstock is presented. The mechanical properties of the cast parts subjected to a specific heat treatment were evaluated. As part of the joint effort between Alcan International Limited and the National Research Council of Canada (NRC), the fatigue results obtained from the semi-solid AA-6061 die cast parts will be also reported.

Abstract: As part of the foundry technology program, Alcan is developing a liquid-based slurrymaking process known as the SEED technology for semi-solid forming. The technology is presently entering the industrial and commercial stages, and will be used by the first customers in late 2006. The semi-solid process offers many advantages to economically fabricate near-net-shape parts having superior quality. The SEED process helps to overcome problems experienced with thixocasting and especially the high cost of feedstock. The SEED process involves two main steps: 1) heat extraction to achieve a desired liquid/solid mixture, and 2) drainage of an excess liquid to produce a self-supporting semi-solid slug that is formed under pressure. An overview of the industrial SEED technology advantages such as the alloy processing flexibility (A356, AA6061) and large slug dimensions and weights, is presented. The influence of the SEED processing parameters (slurry preparation) on the final mechanical properties and the microstructure evolution is also reported.

Abstract: A novel method is introduced to investigate the macro-segregation in 356 Al-Si alloy. In this method, a portion of the remaining liquid is extracted during solidification of the alloy from the bottom orifice of a cylindrical sample. Different parts of the sample plus the extracted material are chemically analyzed and a good correlation between the chemical composition and the predicted values from binary Al-Si diagram was obtained. Comparing the chemical composition of the decanted alloy in the cast piece with those of the 356 standard range has shown that even with 15% of the liquid extraction, the composition of the alloy is still within the intended range.