Thermal Treatment of Aviation Aluminum Alloys in Strip Processing Lines

Abstract

For many years now the use of aluminum as a light weight construction material in the aviation and automotive industry is on the rise. Without the innovative aluminum materials the strategies of constructing in light-weight design cannot be implemented. Last but not least this trend is driven by official requirements directing the reduction of greenhouse gas emissions. Aluminum is used both for structural components as well as for external body parts. Aluminum products for these industries have to undergo a production process which includes homogenizing of the ingots, hot rolling and cold rolling. Subsequent to the cold rolling process, the aluminum sheets have to undergo a heat treatment process to regain formability as well as the required material strength. The material properties required by the aviation and automotive industry are achieved in the annealing furnace and downstream cooling equipment. Equal and well-aimed heating and cooling along the length and across the width provide the strips with the metallurgical properties with regard to hardness and grain size. Hence the annealing furnace and the downstream cooling equipment are the decisive process components and critical for the high quality of the end material. First the material is heated up to a temperature above 500 °C for the solution heat treatment process. The following process step foresees cooling down the material to ambient temperature. Especially 6xxx automotive-alloys as well as 2xxx and 7xxx aerospace-alloys require high cooling rates. Eventually, the material gets heated up again for a certain time to apply an artificial aging process. In floatation heat treatment furnaces the strip is guided sinusoidal and contactless by floatation nozzles through the furnace. The strip is heated up and kept at the required strip temperatures in time, so the aluminum-alloy obtains their structure. The cooling process with high cooling rates is executed as a combination of water and air cooling. A mathematical model calculates the necessary settings for the annealing and cooling process under consideration of the mechanical properties. Paper and presentation will introduce the furnace technology for aluminum strips. Especially, the heat treatment facilities for heat and chemical treatment lines will be presented. It will especially emphasize on heat treatment cycles, the materials and the applications.