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Different morphology and thinning cases of the weld zone of a 7022 aluminum alloy in friction stir welding were analyzed. Metal plastic flow processes in the contact zone for an aerospace friction stir-joint 7022 aluminum alloy were evaluated. The cross section of the contact zon was analyzed by metallographic and tool microscopes. Then, the plastic flow law of the contact zone was established. Theoretical analysis confirmed the validity of the metal plastic flow law and corresponding thinning model of the weld zone. The thinning model for filling due to indirect extrusion–vortex flow can adequately characterize the plastic flow of metals and formation process of thinning in the weld zone. [ABSTRACT FROM AUTHOR]

The properties of hot-dipping A359 aluminum alloys can be improved by strategically placing the S45C steel inserts to locally improve properties such as oxidation and corrosion resistance, but soft A359 aluminum alloy can be easily worn out and thus decreased the S45C steel's reliability. In this study, we have been added 20 wt.%Ni to increases the hardness of the A359 aluminum alloy, then hot dipped the S45C steel into the molten A359-20 wt.%Ni aluminum alloy for 1 min and then heat treated at 400-600 °C. The effect of nickel on the interface characteristic (including kinetic and shear strengths of interface between the S45C steel and aluminum alloy) and the surface glossiness and wear property of the A359-Ni aluminum alloy is also discussed. The experimental results show that the Fe2Al5 intermetallic compound thus the activation energy of the compound formation in the A359-20 wt.%Ni aluminum alloy, and its thickness increased with an increase in heating temperature. Nickel hindered formation of the Fe2Al5 intermetallic compound thus the activation energy of the compound formation in the A359-20 wt.%Ni aluminum alloy (0.413 eV) is larger than A359 aluminum alloy. The nickel could increase the surface glossiness and anti-wear of the hot-dipped coating layer, but they would not deteriorate the interface shear strength. [ABSTRACT FROM AUTHOR]

A novel soft variable polarity plasma arc has been proposed to solve the problems in horizontal welding of aluminium alloys (in 2G position). It is defined as an arc with reduced arc pressure while retaining the ability to maintain a stable keyhole. In this paper, its characteristics were studied and its influence on the stability of keyhole was investigated. The results indicate that it has been changed in the energy and pressure distribution compared with ordinary variable polarity plasma arc. It is beneficial for the stability of keyhole especially for the stability of keyhole shrinking process. The keyhole can be established easily. It can also improve the wetting and spreading of molten metal in weld pool. The reason for a stable keyhole is that the soft variable polarity plasma can provide a suitable heat input and a suitable arc pressure. [ABSTRACT FROM AUTHOR]

The main purpose of this paper is to determine the optimum operating conditions of friction stir welding dissimilar metals joints, namely AA6061 aluminium alloy and SS400 low carbon steel. The optimum operation is the combination of four mainly controllable process parameters for the best quality of uncontrollable parameters, such as both interface and welded zone impact values. In this paper, the V-notch impact value represents the interface toughness and the C-notch impact value for welded zone toughness. Moreover, the possible failure type can be analysed by observing the fractured surface after impact test. The best bending toughness of dissimilar metals joints is produced by the combination of the tool rotation speed of 550 rev min–1, the transverse speed of 0·9 mm s–1, the tool tilting backward 2° angles, and the tool pin diameter of 6 mm. [ABSTRACT FROM AUTHOR]

Intermetallic layer of dissimilar tungsten inert gas welding–brazing butt joint of aluminium alloy/ stainless steel has been studied. A visible unequal thickness intermetallic layer has formed in welded seam/steel interface, and the thickness of the whole layer is <10 μm. The interface with Al–12Si filler metal consists of τ5-Al8Fe2Si layer in welded seam side and θ-(Al,Si)13Fe4 layer in steel side with the hardness values of 1025 and 835 HV respectively, while the interface with Al–6Cu filler metal consists of θ-Al13(Fe,Cu)4 layer with the hardness of 645 HV. The average tensile strength of the joint with Al–12Si filler metal is 100–120 MPa, and the fracture occurs at θ-(Al,Si)13Fe4 layer, while the joint with Al–6%Cu filler metal presents high crack resistance with tensile strength of 155–175 MPa, which reaches more than 50% of aluminium base metal strength. [ABSTRACT FROM AUTHOR]

Eight millimetre thick 2014-T6 Al alloy has been successfully friction stir welded. The experimental results showed that the weld tensile strength differs at different welding parameters. The maximum ultimate tensile strength, which equals to 78% that of base metal, was obtained at a rotating speed of 400 rev min-1 and welding speed of 100 mm min-1. For a specific welded joint, different region of the joint has different tensile strength, which depends on the microstructure variation and microhardness distribution. This is attributed to different thermomechanical actions on different regions of the joints. For the joint with three layers and without defects, the mechanical properties of middle layer are the weakest while the upper layer is the strongest. For the joints with crack or void defect, the position of the defect will be the source of fracture. [ABSTRACT FROM AUTHOR]

Two technical approaches for keyhole closure were conducted. Workpieces of aluminium alloy 2219 were welded using variable polarity vertical up plasma arc welding technology. Effects of welding process parameters on keyhole closure were analysed. Appropriate technical criteria for keyhole closure in the welding of aluminium alloys (3 or 6 mm in thickness) via the variable polarity vertical up plasma arc welding technique were obtained. Experimental simulation of girth welding (overlap welding) was conducted using the appropriate process parameters for the keyhole closure stage of plate butt welding, and the feasibility of circumferential welding was verified. Accordingly, girth welding of the external tank of a carrier rocket was achieved using the appropriate parameters for the keyhole closure technique. In addition, the metallurgical process and mechanical performance for the single pass and overlap welds were analysed and compared. [ABSTRACT FROM AUTHOR]

The report involves a study of the microstructure of tensile, impact and three-point bending samples of aluminum alloy/SiC(p) composites produced by die casting. The results show that in impact samples, 80 μm SiC particulates cluster along the left and right edges of the section vertical plane with the notch plane, and near the notch. In tensile and three-point bending samples, they were distributed uniformly in the matrix. Furthermore, porosities occurred near the notch in the impact samples. The 80 μm SiC particulates will undergo settling in the shot biscuit. There exist arc and irregular shapes in the clustering section of the particulate. The dendrite arm spacing (DAS) is larger in this section. From the shot biscuit to the bending section of the sprue; the quantity of SiC particulate is less. The SiC particulate is clustered in the protrusive region where the injector pins are situated. We can decrease the porosity of die casting samples effectively by designing the overflow well in a wave shape. We can prevent the melt from adhering to the surface of the mold cavity, thermal cracking on the surface of die casting samples and wear on plungers using electroless nickel plating on the SiC particulate. [ABSTRACT FROM AUTHOR]