Experimental evaluation of strain and strain rate during rapid cooling friction stir welding of pure copper

Abstract

The strain and strain rate during friction stir welding was evaluated by measuring the distortion of the marker material. A thin Cu-40Zn foil as marker was inserted into the butting surface of two pure copper workpieces and the tool 'stop action' was employed. The results show that the strain in the shoulder-affected zone increases in a two stair-step shape as the material flows from the front to the rear of the tool, corresponding to the first accelerated and then decelerated flow stages. However, the strain at the two stages has opposite directions. In other words, a strain reversal occurs. Accordingly, the strain rate in the shoulder-affected zone varies in a sinusoidal shape. In the probe-affected zone, there is no obvious strain reverse occurring due to the formation of banded structures. The average strain rate during the band formation is significantly higher than the maximum strain rate in the shoulder-affected zone.

Strain Accumulation and Microstructural Evolution During Friction Stir Welding of Pure Magnesium

“…The deformation status of pure Mg material at different positions can be obtained according to the shape and size of the marker. Compared with the study of Liu et al (2019b), there exists obvious difference in the flow behavior of metals, resulting in different deformation states of the markers on the upper and lower surfaces. The appearance of this phenomenon is related to the nature of the material itself, which is affected by the shape of the stirring probe and the processing parameters (Han et al, 2019).…”

“…Nevertheless, the strain could not be obtained directly but reversely derived from the strain rate. Liu et al (2019a;2019b) developed an experimental method by inserting the marker to approximately determine the strain and strain rate during FSW process of pure copper. However, the detailed microstructural evolution was not involved in this study.…”

Progress in Thermomechanical Analysis of Friction Stir Welding

“…It is environmentally friendly (a green process) because there are no toxic fumes and radiation. Therefore, FSW has been widely used in joining highstrength aluminum alloys and other difficult welding metals in aerospace, shipbuilding, automobile and railway industries [2][3][4]. Due to the remarkable success of FSW, the friction stir concept has been further modified, improved and refurbished to develop various novel material joining and processing technologies for other sophisticated applications [5].…”

Application of nanoindentation to evaluate the hardness and yield strength of brass joints produced by FSW: microstructural and strengthening mechanisms

“…In recent years, FSW of copper and it alloys (specially the CuZn or brass alloys) has been investigated by researchers [6][7][8][9][10][11][12][13][14][15][16]. For example, Heidarzadeh et al [6] have compared the FSW of single and double phase brass alloys.…”

“…They have shown discontinuous dynamic recrystallization (DDRX) in conjunction with annealing twinning is the grain structure formation during FSW. Liu et al [12] have evaluated the strain and strain rate during rapid cooling friction stir welding of pure copper. Their results showed that the strain in the shoulder-affected zone increases in a two stair-step shape as the material flows from the front to the rear of the tool, corresponding to the first accelerated and then decelerated flow stages.…”