Thick AA6061-T6 Research Articles

Al2O3-fortifed AA6061-T6 joint produced via friction stir welding: The effects of traveling speed on microstructure, mechanical, and wear properties

In this study, 6 mm thick AA6061-T6 alloy was friction stir-welded at different traveling speeds while Al2O3 nano-particles were incorporated between adjoining plates. All joints were investigated macro- and micro-structurally. In addition, distribution pattern of Al2O3 nano-particles in the stir zone was observed via scanning electron microscopes. Although the specimen friction stir-welded at 40 mm/min exhibited the most homogeneous particles distribution, friction stir welding at 1600 rpm and 45 mm/min yielded highest tensile strength. Fractographs achieved from tensile test specimens were in close agreement with corresponding percent elongations. Surprisingly, the foregoing specimen exhibited inferior hardness to the as-received AA6061-T6 alloy. Accordingly, it was concluded that dissolution of strengthening precipitates dominated the effect of hard reinforcement particles on enhancement of hardness value. As a result of Al2O3 nano-particles introduction, on the other hand, wear resistance improved tremendously.

Impact Welding of Aluminum Alloys 6061 and 5052 by Vaporizing Foil Actuators: Heat-Affected Zone Size and Peel Strength

Abstract Joining aluminum alloy sheets is increasingly important in manufacturing. Traditional welding techniques create a heat-affected zone (HAZ) around the joint; however, solid-state joining methods such as impact welding produce joints without significant heat. Here, electrically vaporized foil actuators (VFA) provided the high-pressure pulses needed for impact welding. 0.96 mm thick AA6061-T6 and 0.76 mm thick AA5052 were joined in lap and spotlike configurations, at a variety of impact velocities. The welds failed in coach-peel outside the joint interface. The 5052 hardened within 100 μm of the interface. The 6061-T6 may have softened slightly within 50 μm of the interface.

Process operational windows and industrialization scenarios for assembly of large aluminium structures by robotic friction stir welding

In this work, friction stir welding (FSW) of 3.18 mm thick AA6061-T6 sheets in the butt- and lap-joint configuration was investigated with the objective of industrializing the process using low-cost serial industrial robots. The influence of weld pitch on the welding defects, microstructure, hardness, and bend performance of butt and lap welds was examined to identify process operational windows for both joint types. In parallel with these trials, a methodology based on kinetostatic analysis was developed to identify and evaluate viable robotized scenarios for FSW. On the basis of the experimental FSW process development results, this methodology was then applied to identify optimized FSW scenarios for the fabrication of large integrated AA6061 structural components with stringer-to-skin and skin-to-skin joints. Candidate workcell layouts are also presented.

Modeling of Cold Metal Transfer Spot Welding of AA6061-T6 Aluminum Alloy and Galvanized Mild Steel

In this article, a three-dimensional (3D) transient unified model is developed to simulate the transport phenomena during the cold metal transfer (CMT) spot welding process of 1 mm thick aluminum AA6061-T6 and 1 mm thick galvanized mild steel (i.e., AISI 1009). The events of the CMT process are simulated, including arc generation and evolution; up-and-down movement of electrode, droplet formation and dipping into the weld pool; weld pool dynamics; zinc evaporation, and zinc vapor diffusion in the arc. The effects of the gap between the two workpieces and effects of zinc vapor evaporated from the steel surface on CMT process are studied. The results show that the arc temperature, velocity, and pressure keep changing during the CMT process, which is related to the variations of welding current, arc length, and zinc evaporation. It is found that the zinc evaporation leads to the extremely high arc pressure and the upward flow of zinc vapor near the steel surface, which would induce the arc instability and provide the drag force for the droplet impingement. The presence of the gap between the two workpieces can improve the expansion of the arc plasma, resulting in the smaller arc pressure and the more intensive upward flow of zinc vapor from the steel surface. The phenomena observed in the experiment are in agreement with the modeling results.

Process Window for Friction Stir Lap Welding of Aluminum Alloy 6061

Precipitation-hardenable 6xxx series aluminum alloys are incorporated in many structural components with due consideration of their good combination of properties including a relatively high strength, outstanding extrudability and excellent corrosion resistance. Accordingly, AA6061 has been identified as a very good candidate material for structural lightweighting of transportation vehicles. However, the weldability of aluminum alloy (AA) 6061 by means of conventional technologies such as GMAW and GTAW methods is limited by sensitivity to solidification cracking. In this respect, friction stir welding (FSW) presents a tremendous potential for assembly of aluminum structures for the transportation industry due to the low heat involved that can mitigate crack formation and, thus, translate into improved mechanical performance of the assembly. In this work, FSW of 3.18 mm thick AA6061-T6 sheets in the lap joint configuration was investigated. This configuration is considered to be more challenging for assembly by FSW than the butt joint type due to the orientation of the interface with respect to the welding tools and the necessity to break the oxide layer on two aluminium alloy planar surfaces. Weld trials were performed to examine the influence of the FSW tool geometry and process parameters on the welding defects, microstructure, hardness and bend performance. Unacceptable material expulsion and/or significant thinning in one of the two overlapped sheets were produced under most conditions. A set of FSW tool geometries leading to a viable process operational window under which the risk of defects could be mitigated and/or eliminated was identified in this study.

Optimization of Friction Stir Welding Tool Advance Speed via Monte-Carlo Simulation of the Friction Stir Welding Process.

Recognition of the friction stir welding process is growing in the aeronautical and aero-space industries. To make the process more available to the structural fabrication industry (buildings and bridges), being able to model the process to determine the highest speed of advance possible that will not cause unwanted welding defects is desirable. A numerical solution to the transient two-dimensional heat diffusion equation for the friction stir welding process is presented. A non-linear heat generation term based on an arbitrary piecewise linear model of friction as a function of temperature is used. The solution is used to solve for the temperature distribution in the Al 6061-T6 work pieces. The finite difference solution of the non-linear problem is used to perform a Monte-Carlo simulation (MCS). A polynomial response surface (maximum welding temperature as a function of advancing and rotational speed) is constructed from the MCS results. The response surface is used to determine the optimum tool speed of advance and rotational speed. The exterior penalty method is used to find the highest speed of advance and the associated rotational speed of the tool for the FSW process considered. We show that good agreement with experimental optimization work is possible with this simplified model. Using our approach an optimal weld pitch of 0.52 mm/rev is obtained for 3.18 mm thick AA6061-T6 plate. Our method provides an estimate of the optimal welding parameters in less than 30 min of calculation time.

Improvement in Fatigue Strength of Friction Stir Welded Aluminum Alloy Plates by Laser Peening

Plane bending fatigue testing was performed to study the fatigue properties of friction stir welded (FSW) 3 mm thick AA6061-T6 aluminum alloy plates. Fatigue cracks propagated with bends and curves on the specimens, showing large deviation from a linear line. This might be reflecting the material flow and microstructure in the weld zone. The fatigue strength of the unwelded base material (BM) was 110 MPa at 107 cycles and FSW deteriorated it to 90 MPa. However, laser peening (LP) restored the degraded fatigue strength up to 120 MPa which is higher than that of the BM.

Friction Self-Piercing Riveting of Aluminum Alloy AA6061-T6 to Magnesium Alloy AZ31B

Implementation of lightweight low-ductility materials such as aluminum alloys, magnesium alloys and composite materials has become urgently needed for automotive manufacturers to improve the competitiveness of their products. However, hybrid use of these materials poses big challenges to traditional joining process. Self-piercing riveting (SPR) is currently the most popular technique for joining dissimilar materials and has been widely used in joining all-aluminum and multimaterial vehicle bodies. However, in riveting magnesium alloys, cracks always occur for its low ductility. In this paper, a hybrid joining process named friction self-piercing riveting (F-SPR), which combines mechanical joining mechanism of SPR with solid-state joining mechanism of friction stir spot welding (FSSW) by making rivet rotating at high speed in riveting process, was proposed aiming at joining the low-ductility materials. The effectiveness of the F-SPR process was validated via riveting 1 mm thick AA6061-T6 and 2 mm thick AZ31B. The results showed that the F-SPR process could significantly improve the rivetability of magnesium alloys, and greatly increase the joint strength, comparing with the traditional SPR process.

Mechanism of Weld Formation during Friction Stir Welding of Aluminum Alloy

The present work aims at identification of process parameters for sound weld and to understand the mechanism of material matrix movement and weld formation in friction stir welding (FSW) of aluminum alloy. FSW experiments were conducted on 6 mm thick AA6061-T6 plates using various rotational and welding speeds. The welded plates were cut along the transverse direction to examine the macro defects. The defect size as a function of welding and rotational speed has been studied, and three parameter zones were identified. They are insufficient material flow zone, defects free zone, and excessive material flow zone. The sound zone is identified in the moderate rotational speed range for each welding velocity that occurs between the insufficient and excessive material flow zone. In the insufficient material flow zone, the defect size is found to be inversely proportional to rotational speed, whereas in the case of excessive material flow zone the defect size is directly proportional to rotational speed. As welding velocity increases, rotational speed is to be increased proportionally to form a sound weld. The relation between weld parameters, temperature, matrix movement, and weld formation has been established.

Residual stress measurement on AA6061-T6 aluminum alloy friction stir butt welds using contour method

Residual stress is a crucial factor when assessing the integrity of engineering components and welded assemblies. The internal longitudinal stresses in 4mm and 8mm thick AA6061-T6 aluminum alloy friction stir welding (FSW) specimens are measured with contour method. The measuring procedure of the contour method including specimen cutting under clamps with a wire electric discharge machine, precise contour measurement with a coordinate measuring machine, careful data processing and elastic finite element analysis are introduced in detail. Finally, the longitudinal residual stresses throughout the cut plane for the two joints are mapped, and the through-thickness longitudinal stresses of the two FSW joints are also analyzed. Investigated results show that the contour method can be applied to measure the internal residual stress in thin plates with a thickness of 4mm; the longitudinal stress distribution in the present study is not an apparent M-shaped distribution in the transverse direction; within the weld region, the tensile longitudinal stress in the advancing side is larger than that in the retreating side; the longitudinal stresses are not uniform across the thickness of specimens; the peak tensile longitudinal stresses for both joints reach 168MPa (amount to 61% of the yield strength of AA6061-T6 alloy at room temperature), and appear at a depth of 62.5% thickness at the edge of the tool shoulder in the advancing side of the weld.

Effect of the weld thermal cycles of the modified indirect electric arc on the mechanical properties of the AA6061-T6 alloy

Results of temperature measurements during welding of 12.7 mm thick AA6061-T6 alloy plates by modified indirect electric arc (MIEA) are presented. This study describes the thermal cycles in the heat-affected zone (HAZ) and also in the fusion zone. Depending upon the position of the transducers, the maximum temperatures measured in the HAZ ranged from 308 to 693°C, these measurements were related with the tensile test results and the failure zone reported previously by the authors (Ambriz et al., S&I 2006;11:10–17). It was observed that there is a decrease in the mechanical strength of the welded joints, due to the microstructural changes undergone by the AA6061-T6 alloy in which formation of the β′ occurs according to the time–temperature transformation diagram. The inherent cooling conditions of the weld pool observed for the MIEA technique (single welding pass) have made it possible to establish the characteristics of solidification and microstructure for a specific cooling rate.

Efecto de los ciclos térmicos de soldadura por arco eléctrico indirecto modificado (AEIM) en las propiedades mecánicas de la aleación AA6061-T6

Results of temperature measurements during welding of 12.7 mm thick AA6061-T6 alloy plates by modified indirect electric arc (MIEA) are presented. This study describes the thermal cycles of the heat affected zone (HAZ) and also in the fusion zone. Depending upon the position of the transducers, the maximum temperatures measured in the HAZ range from 308 to 693 °C, these measurements were related with the tensile test results, and the failure zone reported previously by the authors [1]. It was observed that, there is a decrease in the mechanical strength of the welded joints, due to the microstructural changes suffered by AA6061-T6 alloy in which formation of the β’ occurs according to the TTT transformation diagram. The inherent cooling conditions of the weld pool observed for the MIEA technique (only one pass of welding), have permitted to establish the characteristics of solidification and microstructure for a specific cooling rate.