Abstract
The study presents an analysis of wear of tools made of 1.2344 steel and MP159 alloy for the process of obtaining an overlap joint in 1.0 mm and 0.8 mm sheet metal made of 7075 T6 aluminum alloy using friction stir welding (FSW) technology. Tool geometry was designed at the Czestochowa University of Technology. Evaluation of tool wear was conducted based on the measurements of geometry of working area of tools by means of a multisensory meter system and based on the assessment of the working area by means of a stereoscope after individual stages of wear tests. Furthermore, based on the results of a static tensile strength test and metallographic examinations of the specimens sampled from the joints obtained during tool wear tests, the effect of the degree of tool wear on joint quality was also evaluated. Analysis of the results revealed that both the tool made of 1.2344 steel and that made of MP159 alloy were substantially worn, increasing the risk of further use of the tools for the joint material (7075-T6) after obtaining the joint with length of 200m, which suggests their low durability. Furthermore, modification of tool geometry caused by wear led to insignificant improvements in joint strength. Therefore, the results of wear measurement set directions for further modification of tool geometry, also due to the fact that despite a substantial wear, the tools continued to yield high-quality joints without defects. As demonstrated in the study, the type of tool material does not only impact on tool life but also, as it was the case in their geometry, has a significant effect on the quality of obtained joints. Although the tool made of MP159 alloy was worn more than the tool made of 1.2344 steel, it allowed for obtaining the joints with substantially better strength parameters.
Highlights
Friction stir welding (FSW) technology was developed in the early nineties of the 20th century in the Welding Institute in the UK
Science and Technology the FSW technology for joining hard metals represents an exceptional challenge due to the poor availability of tool materials that are capable of withstanding the welding process conditions, while its commercial use is limited by high costs and short life of the tools [1, 15, 16, 20, 21]
Measurements of the geometry of the working part of the tool was made using the OGP Smart Scope FLASH 200 multisensory meter system, whereas wear of the FSW tools was evaluated based on comparisons of the contour of a new tool with the contour of the tool for which the wear was measured after individual research cycles
Summary
Tool wear, which is reflected by the change in geometry and caused by mechanical and thermal load to the working surface of the tool, may result from abrasion, plastic deformation, oxidation, adhesion, chipping etc This can be prevented by using appropriately selected process parameters, right material and anti-adhesive and anti-wear coatings. Tool steels have been popular for FSW tools in the process of welding of magnesium, copper and aluminium matrix composites (AMCs), for which accelerated tool wear have been observed They can be used for joining two different materials (e.g. copper with brass), both in overlap joints and butt joints [2, 5, 7, 8, 9, 19, 23, 24]. Obtaining adequate quality of joints while maintaining low costs of the FSW process requires examinations of specific tool materials and design of new tools
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