Microstructure and mechanical properties of laser welded joints between 2198/2060 Al–Li alloys

Dissimilar Al–Li alloys (2198 and 2060) were laser welded without the addition of filler material. The effects of welding parameters on the formation of the welded joints, microstructure evolution, solute segregation, porosity and their relationships with the mechanical properties of the joint were investigated. It was found that reducing the weld heat input can effectively prevent grain coarsening, while decreasing porosity and reducing the tendency for hot cracking, thereby enhancing the properties of the joint. The dissolution of precipitates such as the T1 phase and θ′ phase in the base metal, and the variations in Cu and Mg content between grain interiors and boundaries, resulted from solute segregation during welding, leading to reductions in the strength of the weld.     

Microstructure and mechanical properties of a new Al–Zn–Mg–Cu alloy joints welded by laser beam

A new type of Al–Zn–Mg–Cu alloy sheets with T6 temper were welded by laser beam welding (LBW). Microstructure characteristics and mechanical properties of the joints were evaluated. Results show that grains in the heat affected zone (HAZ) exhibit an elongated shape which is almost same as the base metal (BM). A non-dendritic equiaxed grain zone (EQZ) appears along the fusion line in the fusion zone (FZ), and grains here do not appear to nucleate epitaxially from the HAZ substrate. The FZ is mainly made up of dendritic equiaxed grains whose boundaries are decorated with continuous particles, identified as the T (AlZnMgCu) phase. Obvious softening occurs in FZ and HAZ, which mainly due to the changes of nanometric precipitates. The precipitates in BM are mainly η′, while plenty of GPI zones exist in FZ and HAZ adjacent to FZ, in the HAZ farther away from FZ, η phase appears. The minimum microhardness of the joint is always obtained in FZ at different times after welding. The ultimate tensile strength of the joint is 471.1 MPa which is 69.7% of that of the BM. Samples of the tensile tests always fracture at the FZ.     

Microstructure and tensile properties of laser beam welded Ti–22Al–27Nb alloys

Ti–22Al–27Nb alloys were welded using the laser beam welding process. The microstructure characterization and the tensile properties of the laser beam welded joints were investigated. The experimental results showed that a well-quality joint could be obtained using laser beam welding method. The fusion zone of the welded joint was composed of B2 phase. The tensile strength of the joints at room temperature was basically comparable to that of the base metal and the tensile ductility of the joints achieved 56% of the base metal. The average tensile strength of the welded joints at 650 °C was tested to be about 733 MPa, with the elongation of 2.93%.     

Microstructure and mechanical properties of Mg–9Li–3Al–xGd alloys

The influence of gadolinium on the microstructure and mechanical properties of Mg–9Li–3Al alloy was investigated. Results show that the addition of Gd can effectively refine the α-Mg phase and change the morphology of the α-Mg phase. Meanwhile, the Al₃Gd phase is mainly distributed at the boundaries of the α-Mg phase and inside the α-Mg phase. The mechanical property tests reveal that the addition of Gd can effectively improve the mechanical properties of the as cast alloys. When the content of Gd is 2·0%, the tensile strength and yield stress (engineering stress) reach max values of 188 and 174 MPa respectively. When the content of Gd addition is 2·5%, the elongation of the alloy is 15·7%.     

Microstructure and mechanical properties of Al–Si–Mg–Cu–Ti alloy with trace amounts of scandium

The effect of Sc on the microstructure and mechanical properties of Al–Si–Mg–Cu–Ti alloy was investigated. Results obtained in this research indicate that, with increasing Sc content, the microstructure of the investigated alloys exhibits finer equiaxed dendrites with rounded edges and the morphology of the eutectic Si shows a complete transition from a coarse needle-like structure to a fine fibrous structure upon modification of eutectic Si. Subsequent T6 heat treatment had further induced the precipitation of nano-scaled secondary Al₃(Sc, Ti) phase, as well as spheroidisation of eutectic Si. Combined with T6 heat treatment, the ultimate tensile strength, yield strength, percentage elongation and hardness were achieved in 0.20?wt-% Sc-modified alloy.     

Atomic bonding and mechanical properties of Al–Li–Zr alloy

The atomic bonding of Al–Li alloy with minor Zr is calculated according to the “Empirical Electronic Theory in Solids”. The result shows that the stronger interaction between Al and Zr atoms, which leads to form the Al–Zr segregation regions, promotes the precipitation of Al₃Zr particles and produces a remarkable refinement of Al₃Li grains in the alloy. Because there are the strongest covalent Al–Zr bonds in Al₃Zr and Al₃(Zr, Li) particles, these covalent bonds can cause a great resistance for dislocation movement, and is favorable to strengthen the alloy. On the other hand, with precipitating the Al₃(Zr, Li) particles, it causes the coherent interphase boundary energy of Al/Al₃Li to decrease, and atomic bonding is well matched in between the interface of two phases.     

Microstructure and mechanical properties of friction stir welded 7136–T76 aluminium alloy

Abstract

The microstructure of the weld was examined by light and electron microscopy (scanning and transmission). The various regions, i.e. thermomechanically affected zone, heat affected zone and unaffected base material, were studied in detail to better understand the microstructural evolution during friction stir welding and its impact on basic mechanical properties. The change in morphology of the strengthening phases reflected the relative temperature profile and the amount of deformation across the welded joint during the stir welding process. The centre of the weld was composed of fine grains and coarse particles identified mainly as MgZn₂. In the thermomechanically and heat affected zones, the grain size was not uniform, and the strengthening phases filled the grain interiors, while grain boundaries were surrounded by precipitation free zones. The size of the strengthening phase decreased towards the base material. The hardness profile of the friction stir weld displayed the lowest hardness on the retreating side. Tensile properties of the weld itself were superior to those for material containing weld.     

The microstructure and mechanical properties of friction stir welded Al–Zn–Mg alloy in as welded and heat treated conditions

High strength aluminium alloys generally present low weldability because of the poor solidification microstructure, porosity in the fusion zone and loss in mechanical properties when welded by fusion welding processes which otherwise can be welded successfully by comparatively newly developed process called friction stir welding (FSW). This paper presents the effect of post weld heat treatment (T₆) on the microstructure and mechanical properties of friction stir welded 7039 aluminium alloy. It was observed that the thermo-mechanically affected zone (TMAZ) showed coarser grains than that of nugget zone but lower than that of heat affected zone (HAZ). The decrease in yield strength of welds is more serious than decrease in ultimate tensile strength. As welded joint has highest joint efficiency (92.1%). Post weld heat treatment lowers yield strength, ultimate tensile strength but improves percentage elongation.     

Microstructure evolution and mechanical properties of Mg–9Li–3Al–2Sr alloy in change channel angular pressing

Change channel angular pressing is a specially designed continuous processing technique to prepare bulk ultrafine grained materials. The extrusion process and structure evolution of Mg–9Li–3Al–2Sr alloy were analysed. The long strip phases of α-Mg and β-Li were sheared into short pieces during extrusion. The continuous distribution Al₄Sr phases were extruded into small particles, which are mainly observed in the α/β phase interface and β-Li matrix phase. Structure homogeneity can be achieved, and the mechanical properties were improved with one pass processing. The effect of Al₄Sr phase on the microstructure and mechanical properties of Mg–9Li–3Al–2Sr alloy was observed to be different due to the various extrusion modes and parts.     

Microstructure and mechanical properties of Al–Si cast alloy with additions of Zr–V–Ti

The microstructure and tensile properties at temperatures up to 300 °C of an experimental Al–7Si–1Cu–0.5Mg (wt.%) cast alloy with additions of Ti, V and Zr were assessed and compared with those of the commercial A380 grade. The microstructure of both alloys consisted of Al dendrites surrounded by Al–Si eutectic containing, within its structure, the ternary Al–Al₂Cu–Si phase. Whereas the Al₁₅(FeCrMn)₃Si₂ phases were present in the A380 alloy, Ti/Zr/V together with Al and Si phases, Al(ZrTiV)Si, were identified in the experimental alloy. As a result of chemistry modification the experimental alloy achieved from 20% to 40% higher strength and from 1.5 to 5 times higher ductility than the A380 reference grade. The role of chemistry in improving the alloy thermal stability is discussed.     

Microstructure and mechanical properties of Mg–8Li–xAl–0.5Ca alloys

The effect of the Al content on the microstructure and mechanical behaviour of Mg–8Li–xAl–0.5Ca alloys is investigated. The experimental results show that an as-cast Mg–8Li–0.5Ca alloy is mainly composed of α-Mg, β-Li and granular Mg₂Ca phases. With the addition of Al, the amount of α-Mg phase first increases and then decreases. In addition, the intermetallic compounds also obviously change. The microstructure of the test alloys is refined due to dynamic recrystallisation that occurs during extrusion. The mechanical properties of extruded alloys are much more desirable than the properties of as-cast alloys. The as-extruded Mg–8Li–6Al–0.5Ca alloy exhibits good comprehensive mechanical properties with an ultimate tensile strength of 251.2?MPa, a yield strength of 220.6?MPa and an elongation of 23.5%.     

Microstructure and mechanical properties of Mg–6Li–xAl–0.8Sn alloys

As-cast and as-extruded Mg–6Li–xAl–0.8Sn (x?=?0, 1, 3 and 5?wt-%) alloys were prepared. The microstructure and mechanical properties were investigated and discussed. The experimental results show that the Mg–6Li–0.8Sn alloy is composed of three phases: α-Mg, Mg₂Sn and Li₂MgSn. With the addition of Al, the test alloys display typical α-Mg?+?β-Li duplex structures. The new Mg₁₇Al₁₂ and LiMgAl₂ phases were found in the Mg–6Li–1Al–0.8Sn alloy. The lamellar-type AlLi phase was formed whereas the Mg₁₇Al₁₂ phase disappeared in Mg–6Li–3Al–0.8Sn alloy. The LiMgAl₂ phase vanished in the Mg–6Li–5Al–0.8Sn alloy. The mechanical properties of as-extruded alloys were remarkably improved. The as-extruded Mg–6Li–3Al–0.8Sn alloy exhibited the best mechanical properties, with a yield strength, tensile strength and elongation of 209.8?MPa, 242.6?MPa and 15.5%, respectively.     

Microstructure and mechanical properties of as aged Mg–3Sn–1Al and Mg–3Sn–2Zn–1Al alloy

Effect of Zn on the microstructure, age hardening response and mechanical properties of Mg–3Sn–1Al alloy which is immediately aged at 180°C after extrusion process (T5) was investigated. It was found that the Zn can refine the microstructure, remarkably improve the aging response with the peak hardness increases to 75 HV and the time to peak hardness reduces from ～110 to ～60 h, which is attributed to the solid solution hardening of Al, Zn and an amount of finer Mg₂Sn precipitates. The as aged Mg–3Sn–2Zn–1Al alloy exhibits better mechanical property at room temperature or 150°C than that of Mg–3Sn–1Al alloy, which is ascribed to the fine grained microstructure and thermally stable Mg₂Sn particles dispersed at grain boundaries and in the matrix.     

Thermal properties of Mg–Li and Mg–Li–Al alloys

Abstract

The present work is a study of the thermal properties of Mg–xLi–y Al with x= 4, 8 and 12 wt-% and y= 0, 3 and 5 wt-% as a function of temperature in the range 20–375°C. The thermal diffusivity and coefficient of thermal expansion (CTE) have been measured and the thermal conductivity calculated. The thermal diffusivity of all alloys decreases with an increasing content of lithium. The CTE of the single phase alloys Mg–4Li and Mg–12Li has a linear character, and the CTE of Mg–12Li is higher than that of Mg–4Li. The influence of thermal stresses in the two phase alloy Mg–8Li is perceptible in terms of temperature dependence of the CTE. In Mg–4Li–3Al and Mg–4Li–5Al, an influence of the solution of AlLi phase on all the studied thermal properties has been found.     

Microstructure and mechanical properties of directionally solidified Mg–Zn alloy as a biomaterial

Directionally solidified Mg-4wt-% Zn alloy was prepared and the effect of growth rate on its microstructure evolution and mechanical properties was investigated. A typical cellular structure was observed when the growth rate was lower than 60?µm?s^?1. The microstructure evolved from cell to columnar dendrite as the growth rate increased. The ultimate tensile strength of the directionally solidified alloy was found to be higher than that of the alloy ingot with the same cooling rate. The ultimate tensile strength of the directionally solidified alloy increased with increasing growth rate but it decreased during the cell–dendrite transition. The results indicate that the mechanical properties of the directionally solidified alloy with fine cellular and columnar dendritic structures meet the requirements of biomaterials.     

Microstructure and tensile properties of squeeze cast Al–Zn–Mg–Cu alloy

Abstract

It is well known that wrought aluminium alloys have tensile properties superior to those of the cast products. Wrought grade alloys cannot usually be produced by conventional casting processes to attain the same level of tensile properties. However, progress in casting methods in recent years has made it possible to produce wrought alloys by means of squeeze casting techniques. In the present study an Al–Zn–Mg–Cu alloy has been produced by squeeze casting. Tensile properties close to those of wrought products have been achieved by controlling the microstructure, pressure, and other processing parameters.     

Investigation of mechanical properties of advanced Al–Zn–Mg–Cu alloy

Abstract

The mechanical properties of the rapidly solidified 7000 series powder alloy CW 67 were investigated for various extrusion and heat treatment conditions. The principal aim of the work was to ascertain the optimum processing route for peak aged (T6) material. The highest proof stress in the T6 condition was found to be 572 MN m^?2 for material extruded at 325°C and aged for 13·5 h at 120°C after solutionising. The ductility of this material was found to be 13·5%. The fracture toughness was measured in two orientations and found to be approximately 21 MN m^?3/2 in the short transverse direction and 44 MN m^?3/2 in the longitudinal direction. Degassing and hot compaction was found to improve the fracture toughness of the material substantially.

MST/1504     

Microstructure,mechanical properties and corrosion behaviour of Al–Si–Mg alloy matrix/zircon and alumina hybrid composite

In the present study, the effect of reinforcement on microstructure, mechanical properties and corrosion behaviour of aluminium–silicon–magnesium (Al–Si–Mg) alloy matrix hybrid composites reinforced with varying amounts of zircon and alumina has been investigated. Hardness and room temperature compressive tests were performed on Al–Si–Mg alloy as well as composites. Hardness and compressive strength was found to be higher for composites containing 3.75?% ZrSiO₄?+?11.25?% Al₂O₃. Similarly, Al–Si–Mg alloy and its composites were studied for corrosion behaviour in 1 N HCl corrosive media. The weight loss of all the composites was found to decrease with time due to the formation of passive oxide layer on the sample surface. The results obtained indicate that composites exhibit superior mechanical properties and corrosion resistance compared to unreinforced alloy.     

Microstructure and mechanical behaviour of asymmetric extruded Mg–3Al–1Zn alloy sheets

Abstract

Microstructural evolution and mechanical responses of Mg–3Al–1Zn (AZ31) sheet processed by the asymmetric extrusion (ASE) and conventional extrusion (CE) are examined. Mechanical properties of ASE sheets were remarkably enhanced compared with CE samples. This is attributed to the subdivision of the asymmetric extrusion die along the flow passage equipped with a chamfer on one side, which would trigger the angular spread of the basal texture by introducing an asymmetry shear deformation. Moreover, subsequent annealed ASE specimens show a significant weakening of the basal texture and a combination of the superior stretch formability.