Influence of the E-coating process on the mechanical properties of aluminum welds

The properties of the heat affected zone (HAZ) close to the weld are strongly influenced by the weldingprocess and by the post-weld heat treatment. The objective of this work was determining the width and the mechanicalproperties of the HAZ in Cold Metal Transfer (CMT) welded sheets of aluminum alloy EN AW 6063 T6 for three jointconfigurations: 20 mm lap-, 90°- and 45°-joints. During the CMT welding process the temperatures at defined distancesfrom the joint were measured using thermocouples. Since the weld and the HAZ were inaccessible for direct measurements,the temperatures occurring there were calculated with the aid of a finite element model representing the weldingprocess. Dilatometer samples for tensile testing were heated and quenched based on the temperature curves determinedinside the HAZ. Some of these samples were also heat treated according to the electro-phoretic coating (E-coating)process. Hardness measurements revealed that hardness decreases by approx. 1/3 inside of both the weld and the HAZcompared to the uninfluenced sheet metal. Tensile tests confirmed that increasing the temperature peak inside of theHAZ decreases the strength, but increases the strain. However, this effect was less pronounced in the samples exposedto E-coating heat treatment. The weakest zone was found where temperature peaks of approx. 400 °C occurred.

Keywords:

aluminum sheets , welding , E-coating , heat affected zone , mechanical properties