TWI Industrial Member Report Summary 845/2006
By C-M Lee, B Lee and C Goodfellow
The advantages of the Friction Stir Welding (FSW) process, over fusion welding processes (e.g. arc, electron beam and laser) have caught the attention of many industries. In addition to good joint mechanical properties, FSW offers new design opportunities that enable simplified manufacturing. For 2xxx and 7xxx series aluminium alloys used in the aerospace industry, arc welding is not routinely applied because of the susceptibility to liquation and solidification cracking during welding as well as porosity, the loss of mechanical properties and the poor corrosion and stress corrosion cracking (SCC) performance of the joints. Although FSW is ideally suited to joining 2xxx and 7xxx series aerospace alloys to avoid cracking and develop suitable mechanical properties, the corrosion resistance is reduced and SCC susceptibility of friction stir welds in these alloys is increased compared with the parent material.
The effects of welding conditions on the subsequent corrosion behaviour of friction stir welds is not clear. Therefore, there is a need to develop an understanding of the corrosion mechanisms operating on friction stir welds and their relation to the welding heat input. Furthermore, there is a requirement to identify the most suitable techniques and procedures for investigating the corrosion resistance of friction stir welds.
This project aims to determine the effects of the FSW process on the pitting corrosion properties of the weldments in chloride media. The alloy selected for this work was AA7050 in the T-7451 temper condition, which was developed specifically for use in the aerospace industry due to its high strength, high fracture toughness and good resistance to stress corrosion cracking (SCC).
- To quantify the effect of peak weld temperature and heat input on the pitting corrosion resistance of friction stir welds in a 7xxx aluminium alloy and to compare with an arc weld.
- To determine the suitability of segmented weld electrochemical pitting corrosion tests for characterising the corrosion properties of friction stir welds in aluminium alloys.