Effect of welding parameters on nugget zone microstructure and properties in high strength aluminium alloy friction stir welds

Abstract

The effects of the main welding variables, apart form tool design, on the microstructure and properties of the nugget zone in friction stir welds have been investigated for a typical high strength Al alloy (AA7010). It has been found that there is an optimum rotational speed, for a given travel speed, that gives the highest strength and ductility for the nugget zone. As the travel speed is increased, it is necessary to increase the spindle speed to maintain this condition, although the optimum condition does not directly relate to a constant ratio of rotationalto travel speed. This condition coincides with a heat input, for a given travel speed, that gives the maximum level of solute in solution in the nugget and the lowest density of coarse second phase particles. For low travel speeds, this is limited at excessive heat inputs by reprecipitation occurringduring the weld cooling cycles, whereas for high travel speeds incipient melting within the nugget appears to be an important factor.

Recent advances in friction-stir welding – Process, weldment structure and properties

“…The unsteady condition is possible because heat generation is instantaneous while heat transfer takes time. Incipient melting has been reported in the nugget zone at high travel speeds in an aluminium alloy (AA 7100) [105], and locally melted films were observed during the FSW of cast magnesium alloy AZ91 [106].…”

“…The nugget has equiaxed recrystallised small grains and its hardness may be higher or lower than than the base material depending on the grain-size of the base metal. When 4 mm thick copper plates with average grain size of 210 µm were welded at high rpm (1250) and low welding speed (1.01 mm/s) [171], nugget had lower hardness (60-90 HV), compared to base metal (105)(106)(107)(108)(109)(110). Even though grain size decreased from 210 to 100 µm, hardness decreased slightly due to reduction in dislocation density relative to base metal [171].…”

Stationary shoulder FSW for joining high strength aluminum alloys

“…Because in FSW the welding parameters have a large effect on the resultant joint properties (Hassan et al, 2003), it was important to adopt a methodology that allows a systematic comparison to be made between the two processes. Unfortunately this is not as simple as it first appears since, as will be seen below, the optimum process windows were quite different for the FSW and SSFSW methods and they could not therefore be compared with the same welding conditions.…”

Surface Hardening and Microstructural Evolution of High Carbon Steel By Friction Stir Processing

“…The tool used for FSP plays an important role as it is under constant heavy axial load and friction between tool and substrate produces intense heat, keeping in consideration all the factors. Studies on a range of materials confirmed that the quality of FSP and behaviour of material flow mostly depends on substrate's properties as well as on tool's material, shape and dimensions, processing parameters like rotational speed, feed rate, axial force, cooling system, plunge depth and number of passes [6] [7][8] [9][10].The friction generated by Friction stir processing play foremost role in enhancing the properties of substrate through intense modification and localized plastic deformation, thereby reducing and refining the grain size of the substrate [11].C70 is extensively used in the sector of automobile engineering for the fabrication of connecting rods, performance rods, Torsion and stabilizer bars, Railroad rails and bearings of various automobiles and shows potential in the field of shipbuilding industries. The attainment of elevated temperatures plays an important role in the enhancement and modification of a material's properties.…”