Welded AZ31 Magnesium Alloy Joints Research Articles

Effects and distribution of TiC on the nanoparticle strengthening A-TIG welded AZ31 magnesium alloy joints

AZ31 magnesium alloy sheets were A-TIG welded using mixed activating flux, which contained different ratio of TiC nanoparticles (TiCp) and TiO2 powder, as surface coating. From mechanical test, the values of ultimate tensile strength and microhardness increased from 120.2 MPa to 181.7 MPa, 46.4 HV to 84.2 HV, respectively, which mainly resulted from the grain boundary strengthening of α-Mg and the dispersion strengthening of TiCp. The theoretical calculation suggested that the improvement of the yield strength was mainly the combination of the Hall-Petch and Orowan strengthening mechanisms, and the mismatch strain caused by different coefficient of thermal expansion between the matrix and the particles. Numerical simulation showed that the TiCp had a centralized tendency toward middle and bottom part of welding pool and was confirmed by the micro-zone microhardness test results in the fusion zoon.

Effects of graphene nanoplates on microstructures and mechanical properties of NSA-TIG welded AZ31 magnesium alloy joints

The effects of graphene nanoplates (GNPs) on the microstructures and mechanical properties of nanoparticles strengthening activating tungsten inert gas arc welding (NSA-TIG) welded AZ31 magnesium alloy joints were investigated. It was found that compared with those of activating TIG (A-TIG), and obvious refinement of α-Mg grains was achieved and the finest α-Mg grains of fusion zone of NSA-TIG joints were obtained in the welded joints with TiO2+GNPs flux coating. In addition, the penetrations of joints coated by TiO2+GNPs flux were similar to those coated by the TiO2+SiCp flux. However, the welded joints with TiO2+GNPs flux coating showed better mechanical properties (i.e., ultimate tensile strength and microhardness) than those with TiO2+SiCp flux coating. Moreover, the generation of necking only occurred in the welded joints with TiO2+GNPs flux.

Effects of nano-SiC particles on the FSSW welded AZ31 magnesium alloy joints

The microstructure of nano-SiC enhancing friction stir spot welding (FSSW) joint with dwell time of 3 s was characterised by an onion ring structure which consisted of alternate SiC-free zones and SiC-rich zones where SiC particles refined the grains. However, onion ring structure disappeared and SiC particles dispersed homogeneously when dwell time was 5 s. The microhardness of stir zone (SZ) and tensile shear load of SiC enhancing FSSW joint were higher than those of conventional FSSW joints. After heat treatment at 200°C for an hour, grains of the SZ grew substantially and coursed reduction in mechanical properties of joints, while grain size of SZ and tensile shear load of SiC enhancing joint was invariant but the microhardness of SZ increased.

Effects of current on nanoparticle reinforced magnesium alloy welding joints

Effects of welding current on macromorphologies, microstructures and mechanical properties of nano-SiC particles strengthening activating flux tungsten inert gas welded AZ31 magnesium alloy joints were investigated by scanning electron microscope and energy dispersive X-ray spectrometer observations and microhardness and tensile tests. The results showed that SiC particles mainly dwelled in the centre and bottom zone of welding pool. Moreover, with the welding current increasing, the mechanical properties of the welding joints were improved by the increased SiC particles in welding pool, the depth/width ratios of weld pool and the refined α-Mg grain size. However, the α-Mg grains coarsened and the mechanical properties of joints decreased due to excessive heat input in welding process when welding current over 115 A.

Effects of nano-particles strengthening activating flux on the microstructures and mechanical properties of TIG welded AZ31 magnesium alloy joints

Abstract In this paper, AZ31 magnesium alloy joints were processed by nano-particles strengthening activating flux tungsten inert gas (NSA-TIG) welding, which was achieved by the mixed TiO2 and nano-SiC particles coated on the samples before welding tests. The macro/micro structural observation and mechanical properties evaluation of the welding joints were conducted by using optical microscope, scanning electron microscope, energy dispersive X-ray spectroscopy, X-ray diffraction and tension and microhardness tests. The results showed that nano-particles strengthening activating flux effective improved the microstructure, microhardness in fusion zone, ultimate tensile strength of the TIG welding joints. In addition, the chemical reaction between part of SiC particles and AZ31 magnesium alloy produced Al4C3 and Mg2Si in the joints. The Al4C3 performed as nucleating agents for α-Mg and the dispersed Mg2Si and SiC particles enhanced the mechanical properties of the NSA-TIG welding joints. However, large heat input induced by the increase of the surface coating density of the nano-particles strengthening activating flux, increased the α-Mg grain sizes and weakened the mechanical properties of the welded joints. Therefore, the grain size of α-Mg, distribution of β-Mg17Al12, Mg2Si and SiC particles together influenced the evolution of the mechanical properties of the NSA-TIG welded AZ31 magnesium alloy joints.

Effects of welding current on properties of A-TIG welded AZ31 magnesium alloy joints with TiO2 coating

The effects of welding current on the macro-morphology, microstructure and mechanical properties of tungsten inert gas (TIG) welded AZ31 magnesium alloy joints with TiO2 coating were investigated. The results showed that the increase of welding current led to the increase in the depth/width ratio and deteriorated the surface appearance of the welded seams with TiO2 coating. The grain size of α-Mg and the amount of granular β-Mg17Al12 particles in the welded seams also increased. The welded joints with TiO2 coating exhibited a deeper weld penetration and larger grain size compared with the welded joint without TiO2 coating. When the welding current was less than 130 A, the ultimate tensile strength of the welded joints with TiO2 coating increased with the increase in welding current and then decreased when the welding current was greater than 130 A. The average microhardness of the heat-affected zone and fusion zone decreased gradually with the increase of welding current.

Development of novel heating tool friction stir spot welding (HT-FSSW) for AZ31 magnesium alloy

In this work, a new heating tool friction stir spot welding (HT-FSSW) process was developed, and its impacts on the microstructure and mechanical properties of the welded AZ31 magnesium alloy joints were investigated by microstructure observation, tensile tests and microhardness tests. An increase in the heating tool temperature resulted in a decrease in the grain size of the stir zone (SZ) and an increase in the grain size of the thermomechanically affected zone (TMAZ). The rising heating tool temperature also aggrandised the bonded zone width and enhanced the tensile shear load strength per unit area of the HT-FSSW welded joints. With an increase in the heating tool temperature, the microhardness of SZ increased while that of the TMAZ decreased. Moreover, the slope of the Hall–Petch relationship between microhardness and grain size of the TMAZ is larger than that of the SZ.

Effects of SiC on the Strengthening Activated Tungsten Inert Gas (SA-TIG) Welded of Magnesium Alloy

The effects of SiC particles on the morphologies, microstructures, and mechanical properties of tungsten inert gas welded AZ31 magnesium alloy joints with TiO2 flux coating were studied. The results showed that an increase in the amount of the TiO2 coating improved the weld penetration and the depth/width (D/W) ratio of the TIG welded AZ31 magnesium alloy seams. The α-Mg grains of FZ of welded joints refined gradually with the addition of micro-sized SiC (<30%) /nano-sized SiC (<40%) particles in coatings, and then coarsened when more SiC particles added. In addition, the microhardness of the FZ and ultimate tensile strength of the welded joints increased with the addition of SiC particles, and nano-sized particles have more strong efficiency on the improvement of mechanical properties compared with micro-sized SiC particles.

Effects of fluxes on distribution of SiC particles and microstructures and mechanical properties of nanoparticles strengthening A-TIG (NSA-TIG) welded magnesium alloy joints

The effects of fluxes and the size of SiC particles on the morphologies, microstructures and mechanical properties of tungsten inert gas welded AZ31 magnesium alloy joints were investigated. The results showed that addition of SiC particles in the activating fluxes led to the decrease in all the weld penetrations while the surface appearance of welded joints improved in the case of TiO2 activating flux was adopted. Grain refinement was obtained in the welded seams with the addition of SiC particles in TiO2 flux and the effect of nanosized SiC particles on grain refinement is found to be more impressive than that of microsized SiC particles. The microhardness of the fusion zone and ultimate tensile strength of the welded joints increased with the addition of SiC particles in TiO2 activating flux and nanosized particles have more strong efficiency on the improvement of mechanical properties compared with microsized SiC particles. SiC particles did not improve the mechanical properties of A-TIG welded joints with CaF2 activating flux.

Effects of SiC ceramic particles on microstructures and mechanical properties of gas tungsten arc welded AZ31magnesium alloy with Cr2O3 flux coating

The effects of SiC ceramic particles on the macromorphologies, microstructures and mechanical properties of tungsten inert gas welded AZ31 magnesium alloy joints with Cr2O3 flux coating were investigated. The results showed that an increase in the amount of SiC ceramic particles contained in the Cr2O3 flux coating led to the gradual decrease in weld penetrations. The weld penetrations of all welded seams with flux coatings were obviously higher than those without flux coating. Grain refinement was obtained in the welded seams when SiC ceramic particles were added in the Cr2O3 flux coating. With an increase in the amount of SiC ceramic particles, the ultimate tensile strength value of the welded joints increased at first and then decreased. Moreover, the microhardness of the fusion zone increased gradually with an increase in the addition of SiC ceramic particles in the Cr2O3 flux coating.

Effects of mix activated fluxes coating on microstructures and mechanical properties of tungsten inert gas welded AZ31 magnesium alloy joints

The effects of mix activated fluxes on the penetrations, microstructures and mechanical properties of tungsten inert gas (TIG) welded AZ31 magnesium alloy joints were studied. The results showed that an increase in the amount of TiO2 coating improved the weld penetration and depth/width ratio of the TIG welded AZ31 magnesium alloy seams. The α-Mg grains of the fusion zone (FZ) became fine gradually with the addition of CaF2 coating but coarsened sharply when the amount of TiO2 coating was over 70%. In addition, the porosities and total length of solidification cracks in the FZ were reduced by the CaF2 and TiO2 coatings. The ultimate tensile strength value of the welded joints increased with the addition of TiO2 coating but decreased sharply when more TiO2 coating was adopted.

Effects of CaF2 Coating on the Microstructures and Mechanical Properties of Tungsten Inert Gas Welded AZ31 Magnesium Alloy Joints

The effects of CaF2 coating on the macromorphologies of the welded seams were studied by morphological analysis. Microstructures and mechanical properties of butt joints welded with different amounts of CaF2 coatings were investigated using optical microscopy and tensile tests. The welding defects formed in the welded seams and the fracture surfaces were analyzed by scanning electron microscopy. An increase in the amount of CaF2 coating deteriorated the appearances of the welded seams but it improved the weld penetration depth and the depth/width (D/W) ratio of the tungsten inert gas (TIG) welded joints. The α-Mg grains and Mg17(Al,Zn)12 intermetallic compound (IMC) were coarser in the case of a higher amount of CaF2 coating. The increase in the amount of CaF2 coating reduced the porosities and total length of solidification cracks in the fusion zone (FZ). The ultimate tensile strength (UTS) value and elongation increased at first and then decreased sharply.

Effects of TiO2 coating on the microstructures and mechanical properties of tungsten inert gas welded AZ31 magnesium alloy joints

► The weld penetration and the D / W ratio could be improved dramatically by increasing of the amount of the TiO 2 coating. ► The average grain size of the α-Mg grains increased and the β-Mg 17 Al 12 IMC transformed from granular structure to continuous structure with an increase of the amount of the TiO 2 coating. ► With an increase of the amount of the TiO 2 coating, the microhardness of the FZ of the AZ31 magnesium alloy welded joints decreased slightly at first and then decreased sharply. ► The UTS value of the welded joints increased with an increase of the amount of the TiO 2 coating. ► However, too much TiO 2 coating caused a significant decrease of the UTS value of the welded joints. The effects of TiO 2 coating on the macro-morphologies, microstructures and mechanical properties of tungsten inert gas (TIG) welded AZ31 magnesium alloy joints were investigated by microstructural observations, microhardness tests and tensile tests. The results showed that an increase in the amount of the TiO 2 coating resulted in an increase in the weld penetration and the depth/width ( D / W ) ratio of the TIG welded AZ31 magnesium alloy seams. Moreover, the average grain size of the α-Mg grains increased and the β-Mg 17 Al 12 intermetallic compound (IMC) was coarser in the case of higher amount of the TiO 2 coating. With an increase in the amount of the TiO 2 coating, the microhardness of the fusion zone (FZ) of the AZ31 magnesium alloy welded joints decreased slightly initially and then decreased sharply. In addition, with an increase in the amount of the TiO 2 coating, the ultimate tensile strength (UTS) value and elongation of the welded joints increased at first and then decreased sharply.

Impact Properties of TIG Welded AZ31 Magnesium Alloy Joints

Magnesium and its alloys are the lightest among the metallic materials which are in common use, having a high strength-to-weight ratio along with an excellent machinability and a high damping capacity. Because of these characteristics, nowadays they are applied to various structural parts such as aircraft, automobiles, optical and electronic instruments, industrial robot components. TIG welded joints of AZ31 magnesium alloy has high joint efficiency which can be obtained by the selection of optimum welding conditions. If the welded joints of magnesium alloy are applied to the structure materials, it is very important not only the strength of under static load but also the strength of under dynamic load. However, there is only few report about impact properties of welded AZ31 magnesium alloy joints. In this research, AZ31 magnesium alloy plates 6 mm in thickness were welded on butt welding of square groove without root gap and filler wire using TIG welding process. AZ31 magnesium alloy was carried out at various welding conditions. The effects of welding conditions and notch location on impact properties were studied. Impact values of welded joints were nearly equal to those of the base metal, regardless of welding current. In case of the notched specimens of welded joints, crack initiation energy showed slightly lower than crack propagation energy, regardless of notch location. But, unnotched specimens of welded joints, crack initiation energy showed remarkably high value than crack propagation energy. This means, crack initiation energy spent the large amount of total absorbed energy.