M.M.Z. Ahmed

The Use of Bobbin Tools for Friction Stir Welding of Aluminium Alloys

The use of a double sided friction stir welding tool (known as a bobbin tool) has the advantage of giving a processed zone in the workpiece which is more or less rectangular in cross section, as opposed the triangular zone which is more typically found when conventional friction stir welding tool designs are used. In addition, the net axial force on the workpiece is almost zero, which has significant beneficial implications in machine design and cost. However, the response of these tools in generating fine microstructures in the nugget area has not been established. The paper presents detailed metallographic analyses of microstructures produced in 25mm AA6082-T6 aluminium wrought alloy, and examines grain size, texture and mechanical properties as a function of processing parameters and tool design, and offers comparison with data from welds made with conventional tools.

Effect of friction stir welding speed on mechanical properties and microstructure of nickel based super alloy Inconel 718

Abstract In this study, 4 mm thick nickel based super alloy Inconel 718 has been friction stir welded using different traverse speeds of 30, 50 and 80 mm min−1 at a rotation rate of 400 rev min−1. Since the Inconel 718 alloy was friction stir welded in the annealed condition, a significant increase in mechanical properties has occurred. Microstructural evolution in the nugget (NG) zone has been investigated using electron back scattering diffraction (EBSD) at the top surface and near the base of the NG as well as across the transverse cross-section. Low resolution EBSD scan across the NG to the base material showed great reduction in grain size from the base material to the NG region. High resolution EBSD scans showed that the NG region is dominated by dynamically recrystallised grain structure with very fine grains that was varied in size from the top to the base of the NG.

The Effect of Heat Treatment on the Properties of Friction Stir Processed AA7075‐O with and without Nano Alumina Additions

In this study, four passes friction stir processing (FSP) were applied on AA7075-O with and without the incorporation of alumina nano-particles (Al2O3) of average size 40nm. FSP parameters were constant at 500rpm and 40mm/min speed with tilt angle of 30. FSP rotation direction applied on clockwise and then counters clockwise direction every two passes. The friction stir processed (FSPed) materials were section and solution treated at 515C for 1.5hrs that followed by age hardening at 120C for 12, 24 and 36hrs. The effect of heat treatment regimes on the microstructure and hardness were examined. The microstructure and hardness after HT were compared with that of as FSPed material in each case. It has been found that in case of as FSPed material without any HT the effect of nano-alumina particles is significant in hardness increase relative to the one without powder. However, applying heat treatment regime has resulted in a slighter difference in the hardness between the two cases with and without nano particles additions.

Effect of Heat Treatment on Friction-Stir-Processed Nanodispersed AA7075 and 2024 Al Alloys

Friction stir processing (FSP) is gaining wide recognition in producing surfaces with high hardness and enhanced properties for light weight transportation application and armored vehicles. This work compares the effect of T6 peak-aging heat treatment on the toughness properties and the aging precipitation behavior of friction stir processed and nanodispersed AA2024 and AA7075 alloys. Plates of aluminum alloy AA7075-O with and without the addition of alumina nano-particles (Al2O3) of average size ~40 nm were FSP. The AA2024 nanodispersed alloys were prepared by casting, then were FSP. Combining nanodispersion and friction stir processing with peak-aged condition has shown to be an effective route in enhancing the elongation % of AA2024 alloy to double that of the T6 peak aged condition, and improving the impact toughness of AA7075 by 35% compared to the peak aged condition. The presence of nanodispersions affects the precipitation behavior of both AA2024 and AA7075 in peak aged condition, where the precipitates attach themselves to the nanoparticles and spinel type precipitates form resulting de-acceleration of the aging process.