Effect of chemical composition and heat treatment on intergranular corrosion and strength of AlMgSiCu alloys

Abstract

The use of aluminum in chassis, bumper, and crash boxes has increased in the last 10 years with an increase in the production of electric vehicles in the automotive industry. The extrusion process has also gained importance because it allows mass production. While basic 6xxx series aluminum alloys such as 6060 and 6063 were used in the early stages of the process, later on, 6005A and 6082 alloys, which provide higher strength, have been used. Alloys with higher strength and crash ability are needed with an increase in safety requirements in automotive. In this study, the effect of chemical composition and heat treatment on the intergranular corrosion strength of 6056 alloys was examined. Another aim of this study is not only to produce high strength and ductility alloy but also to provide good corrosion resistance as automotives are used in different environments for several decades. The 6056 alloys are potential candidate materials for the new-generation electrical vehicles in the automobile industry due to their high strength, weldability, machinability, and impact resistance. Therefore, in our work, we produced 6056 alloy samples in a billet form using the direct chill casting method. Then they were homogenized, and billets were extruded as a box profile. Experimental studies were carried out on 6056 alloys with two different chemical compositions and three different heat treatment conditions (T42, T62, and T76) using Method B of EN ISO 11846 standard for corrosion testing. Crack sizes of metallographic sections from corroded areas were calculated g using a scanning electron microscope. As a result, we found that the addition of Mg to 6056 alloys improves corrosion resistance, while copper reduces it. When Zn is added to the alloys, Mg starts to react with it and forms MgZn2, which increases the corrosion progress. Moreover, when heat treatment is applied at T76 conditions, the alloys demonstrate high corrosion resistance.