Evaluation and optimization of the metallurgical properties of aluminum billets for extrusion produced from recycling of scrap metal

Abstract

The quality and productivity of the extrusion process of aluminum alloys depends heavily on the raw material used, that’s to say, on the billets obtained through the process of semi-continuous Direct Chill (DC) casting.Although the Brazilian market has a few suppliers of good quality DC billets, their costs of production are very high. This being so, companies which produce extrudes, the vast majority of which are not large businesses, end up relying on small suppliers or on the internal production of ingots (not DC billets), which leads to low quality of the billets and, consequently, to lower productivity and quality in their products. Thus, there is a lack in the production of good quality and low cost billets in the Brazilian extrusion market. In this scenario, the production of DC billets derived from the recycling of scrap metal is an excellent alternative compared to the use of primary aluminum, typically used by the large national producers of billets. The recycling of scrap aluminum also offers a substantial reduction in the consumption of electrical energy. However, the intense use of scrap in the production of billets could bring about problems of quality in the DC billets. The present project focuses precisely on this aspect: the replacement of primary aluminum with recycled aluminum in the smelting load, controlling the process, striving for a quality of billet comparable to the conventional billets obtained by using primary aluminum. The aim is to characterize the metallurgical quality of billets produced by a recently established company which uses an innovative process based on recycled scrap, having as main focus the effects of the use of scrap in the quality of the DC billets produced. To this end, comparisons will be carried out between samples of DC billets produced using recycled scrap and samples of DC billets smelted conventionally, by means of micro and macro structural analyses, as well as heat malleability. It is intended to produce good extrudability in those billets through the study and consequent control of the smelting process, and through the optimization of the thermal treatment of homogenization. (AU)