Advanced Materials Research Vols. 15-17

Abstract: Friction stir welding is being attracted and developed as an efficient joining method in the manufacturing field of Automobile, Aerospace and Ship building industries. As the FSW develops, more scientific research work investigations in this field have also been increased. Recent studies in FSW have revealed that both heat and metal flow characteristics have a non-symmetric complex nature about the tool axis. But until now there is no efficient 3D- heat flow model to be comparable with the experimentally measured values. The body of the work covered FSW of Al6061 and its thermal distribution based on a nonsymmetrical analytical model for the heat input in to the matrix of Al plates from FSW tool due to the effect of combined translation and rotational motion of the tool pin and shoulder. Finally the 3D- finite element heat transfer analysis program has been used to plot the heat distribution at the Friction Stir Welded joint in Al 6061 plate. The work concludes that the heat distribution result obtained from FE analysis has a reasonable agreement with the experimentally measured values.

Abstract: The microstructure and mechanical properties of spot friction stir welded A 5052 alloy were investigated with insertion depth of welding tool. As the insertion depth of welding tool increased, the size of stirring zone increased and the thickness of upper sheet decreased. The value of shear load was the lowest at the shallowest insertion depth and increased to the highest value of 3.35 kN at a 1.6mm of insertion depth. An increase in the pin insertion depth beyond 1.6mm did not result in further increase in the lap shear load. Spot friction stir welded joints showed shear fracture mode at shallower insertion depths and fracture mode changed to plug fracture mode as the insertion depth was deeper.

Abstract: Linear Friction Welding (LFW) of IN-718 Superalloy was investigated under several processing conditions. The influence of process parameters such as frequency (60Hz to 100Hz), amplitude (2mm to 3mm) and frictional pressure (50MPa to 110MPa) on the microstructure and mechanical properties of welded specimens was determined. Optical and scanning electron microscopy, and micro-hardness testing were used to characterize the welded areas as well as the Thermo-Mechanically Affected Zones (TMAZ). In-situ thermocouple measurements were performed to follow temperature evolution in the specimens during the different phases of the LFW process. The analysis of the results indicated that for some specific conditions (f=80Hz, a=2mm and P=70MPa) a maximum temperature of 1200°C was attained during the last stage of the welding process, the burn-off phase. This temperature, very close to the alloy melting range, would be sufficient to cause partial liquation in this zone. Microscopic examinations revealed the presence of oxide particles aligned around the weld interface. Their concentration and distribution, varying with process parameters, affect the weld integrity. The TMAZ characterised by a global loss of strength (from 334HV to 250HV) is associated with temperatures exceeding 800°C and causing γ’ and γ’’ reversion. A narrow band of the TMAZ, exposed to high strains and temperatures, showed evidences of dynamic recovery and recrystallization (up to 67% of reduction in the matrix grain size). Visual and microscopic examination of the flash layer, revealed two distinct zones. Microstructure evolution and microhardness variations were associated to process parameters and the optimum conditions for obtaining defect free weldments were determined.

Abstract: We tried to join steel to Al-Mg alloy using a resistance spot welding method. The effect of Mg in Al-Mg alloy on the strength and the interfacial microstructure of the joint was investigated. Additionally, the effect of insert metal of commercially pure aluminum, which was put into the bonding interface, on the joint strength was examined. The obtained results were as follows. The cross-tensile strength of a joint between SS400 steel and commercially pure aluminum (SS400/Al) was high and fracture occurred in the aluminum base metal. However, the strength of a joint between SS400 and Al-Mg alloy was remarkably low and less than 30% of that of the SS400/Al joint. An intermetallic compound layer developed so thickly at the bonded interface of the SS400/Al-Mg alloy joint that the joint strength decreased. The intermetallic compound layer developed more thickly as Mg content in the Al-Mg alloy increased. Using insert metal of commercially pure aluminum containing little Mg successfully improved the strength of the SS400/Al-Mg alloy joint and the strength was equivalent to that of the base metal.

Abstract: The characterizations on the microstructural and mechanical properties of the Mg-Al-Zn multi-element intermetallic alloys fabricated by friction stir processing (FSP) are presented. The composites of the alloys vary within Mg35-70Al5-25Zn25-45. The maximum working temperature can reach 550oC. The current process applies the FSP on vertically stacked foils of various portions of Mg, Al and Zn, 99.9% in purity and 0.2 to 1 mm in thickness. In order to homogenize the alloy composition, three or more FSP passes in opposite directions are applied. Depending on the relative contents of Mg, Al and Zn, numerous intermetallic compound phases are induced. The resulting intermetallic alloys exhibit high hardness up to 350 Hv.