Microstructure and Mechanical Properties of Friction Stir Welded Dissimilar Aluminum Joints of AA2024-T3 and AA7075-T6

Abstract

Dissimilar aluminum alloys such as 2024-T3 and 7075-T6 plates 3 mm thickness were friction stir butt welded. The welding was carried out at a constant welding speed of 100 mm/min and rotation speeds of 400, 800, 1200, 1600 and 2000 min À1 . Effects of rotation speeds and fixed location of two alloys on microstructures especially the homogeneity of elemental distribution in the stir zone (SZ), hardness distributions, and tensile properties of the joints were investigated. The homogeneity of constituents of the two alloys in the SZ was analyzed by a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectroscopy (EDS).At the lowest rotation speed of 400 min À1 there was no mixing of two alloys in the SZ and a border between them was observed regardless of the fixed location. Increase of rotation speed more than 400 min À1 brought about a mixed structure likewise onion ring with periodic change of equiaxed grain size and heterogeneous distribution of alloying elements in the SZ. At 2000 min À1 of rotation speed the SZ mainly composed of the material fixed on the advancing side. The hardness increased in the zones occupied by 2024-T3 Al alloy and fluctuations took place in the SZ due to the onion ring at the higher rotation speeds till 1600 min À1 . At 2000 min À1 of rotation speed the hardness of SZ mainly depend on the material fixed on the advancing side. Hardness minima was in the heat affected zone (HAZ) on the side of AA2024-T3 Al alloy and the values slightly increased as the rotation speed increased. In the case of transverse tensile test, defect-free joints were fractured at the HAZ on 2024-T3 side and a maximum tensile strength of the joints was achieved at 1200 min À1 of rotation speed when 2024-T3 Al alloy was located on the advancing side. On the other hand, the tensile properties of SZ in the longitudinal direction showed higher values when 7075 Al alloy was located on the advancing side.

Influence of Tool Rotational Speed and Axial Load in Friction Stir Welding (Fsw) of High Strength Aluminum Alloys

“…4). Higher rotational speed caused excessive plastic deformation, high heat input, and then turbulent material flow in the welding zone.These results are in agreement with the reported in literature for similar material [4].Onion ring patterns were observed and are clear at rotational speed value of 800 and 1200 rpm respectively. These bands indicate that good mixing and stirring action between the two base metals in the welding region were occurred.…”

“…This paper interested in studying influence of FSW machine variables such as tool rotary speed, and axial force on microstructure form, and mechanical behaviors of the FS welded joints. [4] discussed the changes in microstructure, tensile properties, and hardness distribution of friction stir welded joints, at different values of rotary speed with replacement of the location of plates. Macrostructure investigation revealed mixed structure and onion ring pattern was formed with increasing rotational speed.…”

Microstructure and failure mechanisms of refill friction stir spot welded 7075-T6 aluminum alloy joints

“…6, when the duration is 3 s, the difference of Vickers hardness is rather small with the increasing of rotational speed. However, when the duration time is 5 s, the difference of Vickers hardness is slightly bigger, which can be attributed to the increasing of heating or cooling rates during welding by increasing duration time, because the increasing heating rate could reduce the time for the precipitates to grow [21].…”

“…Compared to the HAZ, the grains in the TMAZ and SZ undergo severe intense plastic deformation besides frictional heat, especially the SZ undergo dynamic recrystallization, which induces the appearance of fine equiaxed grain structure, meanwhile, the larger amount of precipitates in the SZ were dissolved due to the higher temperature and then reprecipitated during the following natural ageing [21]. Hence the hardness in the SZ and TMAZ can be attributed to the comprehensive effect of variations in the grain sizes and strengthening precipitates.…”

Brazed Joint Interface Bonding Strength of AR500 Steel and AA7075 Aluminium Alloy

“…However, the joining of AR500 steel and AA7075 aluminium alloy is difficult because of the formation of a brittle intermetallic phase and issues associated with the compatibility of the metallurgical properties of both metals. High-strength aluminium alloys in the 2xxx and 7xxx series are also categorized as unweldable materials due to the difficulty of welding them by using conventional fusion welding [19][20]. In recent years, there have been proposals to use high-strength aluminium alloys from the 7000 series, particularly AA7075, in the fabrication of heavy vehicle shell.…”