Improvement of Microstructure and Mechanical Properties of Rapid Cooling Friction Stir-welded A1050 Pure Aluminum

Two-mm thick A1050 pure aluminum plates were successfully joined by conventional and rapid cooling friction stir welding(FSW), respectively. The microstructure and mechanical properties of the welded joints were investigated by electron backscatter diffraction characterization, Vickers hardness measurements, and tensile testing. The results showed that liquid CO_(2) coolant significantly reduced the peak temperature and increased the cooling rate, so the rapidly cooled FSW joint exhibited fine grains with a large number of dislocations. The grain refinement mechanism of the FSW A1050 pure aluminum joint was primarily attributed to the combined effects of continuous dynamic recrystallization, grain subdivision, and geometric dynamic recrystallization. Compared with conventional FSW, the yield strength, ultimate tensile strength, and fracture elongation of rapidly cooled FSW joint were significantly enhanced, and the welding efficiency was increased from 80% to 93%. The enhanced mechanical properties and improved synergy of strength and ductility were obtained due to the increased dislocation density and remarkable grain refinement. The wear of the tool can produce several WC particles retained in the joint, and the contribution of second phase strengthening to the enhanced strength should not be ignored.

Microstructure and mechanical properties of stationary shoulder friction stir welding joint of 2A14-T62 aluminum alloy

2A14-T62 butt joint was successfully welded by stationary shoulder friction stir welding(SSFSW)method.The results showed that using a pin with small shoulder could broaden the process window,and under a rotation speed of 2000 r/min and welding speed of 30 mm/min,joint with smooth surface,small reduction in thickness and little inner defects was obtained.The weld nugget zone was approx-imately circular,which was a unique morphology for SSFSW.The heat-affected zone(HAZ)and thermo-mechanically affected zone(TMAZ)were both quite narrow due to the lower heat input and slight mechanical action of the stationary shoulder.The fraction of high angle grain boundaries(HAGBs)exhibited a“W”shape along horizontal direction(from advancing side to retreating side),and the minim-um value located at HAZ.The average ultimate tensile strength and elongation of the joint were 325 MPa and 4.5%,respectively,with the joint efficiency of 68.3%.The joint was ductile fractured and the fracture surface contained two types of dimples morphology in different re-gions of the joint.Microhardness distribution in the joint exhibited a“W”shape,and the difference along the thickness direction was negli-gible.The joint had strong stress corrosion cracking susceptibility,and the slow stain rate tensile strength was 139 MPa.Microcrack and Al2O3 particulates were observed at the fracture surface.

Influence of Non-Natural Ageing Temperature on the Microstructural Characteristics and Mechanical Properties of Cast Aluminum 6063 Alloy

This research considered the effect of non-natural aging on the microstructural characteristics and mechanical properties of as-cast aluminum 6063 alloys. The samples were developed through a sand casting process and machined into tensile and impact test samples before carrying out solution heat treatment at 550?C (0.83 Tm) on two parts of the samples while retaining one part as the control. The two parts were further divided into sets denoted A and B and were aged at 180?C (0.27 Tm) and 160?C (0.24 Tm), respectively, for 12 hours. The results showed that sample A has the optimal yield strength and ultimate tensile strength of 192 and 206 MPa, respectively. Likewise, the sample gave the highest impact strength value of about 9.63 J/mm2. The observed results were supported by the optical micrograph, which revealed that the sample has evenly dispersed precipitates in its microstructure. This is deemed responsible for the observed increase in strength of the sample.

Influence of samarium content on microstructure and mechanical properties of recycled die-cast YL112 aluminum alloys

The influence of Sm(Samarium) content on microstructure and mechanical properties of recycled die-cast YL112 aluminum alloys was investigated.The results show that many small Sm-rich particles form in the recycled die-cast YL112 alloys with Sm addition.At the same time,the secondary dendrite arm spacing in the YL112 alloys modified with Sm is smaller than that of the unmodified alloy.The eutectic Si of recycled diecast YL112-xSm alloys transforms from coarse acicular morphology to fine fibres,Mechanical properties of the investigated recycled die-cast YL112 aluminum alloys are enhanced with Sm addition,and a maximal ultimate tensile strength value(276 MPa) and elongation(3.76%) are achieved at a Sm content of 0.6wt.%.Due to the modification of eutectic Si by Sm,numerous tearing ridges and tiny dimples on the fractures of tensile samples are observed.

Effects of minor Sc on the microstructure and mechanical properties of Al-Zn-Mg-Cu-Zr based alloys

Five kinds of Al-Zn-Mg-Cu-Zr based alloys with different Sc additions were prepared by ingot metallurgy. The effects of minor Sc on the microstructure and mechanical properties of Al-Zn-Mg-Cu-Zr based alloys were investigated using tensile tests, optical microscopy （OM）, and transmission electron microscopy （TEM）. The results show that the ultimate tensile strength and yield strength are improved by 94 and 110 MPa, respectively, and the elongation to failure remains at a reasonable extent （11.1%） in the Al-Zn-Mg-Cu-Zr based alloy with 0.21 wt.% Sc addition after solution heat treatment at 475°C for 40 min and then aged at 120°C for 24 h. The addition of minor Sc induces the formation of Al3（Sc,Zr） particles, which are highly effective in refining the cast microstructures, retarding recrystallization, and pinning dislocations. The increment of strength is attributed mainly to fine grain strengthening, precipitation strengthening of Al3（Sc,Zr） particles, and substructure strengthening.

Effect of minor Sc and Zr on microstructures and mechanical properties of Al-Zn-Mg based alloys

Two kinds of Al Zn Mg based alloys with and without Sc, Zr addition were prepared by ingot metallurgy. The tensile mechanical properties and microstructures of the studied alloys at different treatment conditions were studied. The results show that addition of minor Sc and Zr can remarkably improve the strength of Al Zn Mg based alloys, but the ductility remains on a higher level. The strength increment is mainly due to fine grain strengthening, substructure strengthening and precipitation strengthening of Al 3(Sc,Zr).

Microstructure and mechanical properties of the joint of 6061 aluminum alloy by plasma-MIG hybrid welding

Plasma-MIG {metal inert gas arc welding） hybrid welding of aluminum alloy with 6 mm thickness using ER5356 welding wire was carried out. The microstructures and mechanical properties of the welded joint were investigated by optical microscopy, X-ray diffraction （XRD） , energy dispersive spectroscopy （EDS） , tensile test, hardness test and scanning electron microscope （ SEM） were used to judge the type of tensile fracture. The results showed that the tensile strength of welded joint was 142 MPa which was 53. 6% o f the strength o f the base metal. The welding seam zone was characterized by dendritic structure. In the fusion zone, the columnar grains existed at one side of the welding seam. The fibrous organization was found in the base metal, and also in the heat affected zone （HAZ） where the recrystallization occurred. The HAZ was the weakest position of the welded joint due to the coarsening of Mg2Si phase. The type of tensile fracture was ductile fracture.

Microstructures and mechanical properties of Al-Mg and Al-Zn-Mg based alloys containing minor scandium and zirconium

A series of Al Mg and Al Zn Mg based alloys with and without Sc, Zr were prepared by ingot metallurgy. The mechanical properties and microstructures of the studied alloys under different treatment conditions were studied. In addition, the existing form and acting mechanism of minor Sc and Zr in Al Mg and Al Zn Mg based alloys were analyzed and discussed. The following conclusions can be drawn. First, adding of minor Sc and Zr to those alloys can increase the strength of Al Mg and Al Zn Mg based alloys by 25%, while the ductility can remain in 15% and 8%, respectively. Second, in Al Mg and Al Zn Mg based alloys, minor Sc and Zr mainly exist in two forms of aluminides containing Sc and Zr, one is Al 3(Sc,Zr) I precipitated from the melt during solidification, the other is Al 3(Sc,Zr) Ⅱ precipitated during homogenization. The former is the most effective grain refiner for α (Al) solid solution matrix, and the latter is coherent with the matrix and can strongly pin dislocations and subboundaries, which can effectively restrain recrystallization of the alloys during hot deformation, annealing and solid solution. Third, strengthening caused by adding minor Sc and Zr to the studied alloys is mainly due to fine grain strengthening, precipitation strengthening and substructure strengthening of Al 3(Sc, Zr) caused by restraining recrystallization.

Effects of retrogression heating rate on microstructures and mechanical properties of aluminum alloy 7050

The effects of the retrogression heating rate(340℃/min,57℃/min,4.3℃/min)on the microstructures and mechanical properties of aluminum alloy 7050 were investigated by means of hardness measurement,tensile properties testing,differential scanning calorimetry(DSC)and transmission electron microscopy(TEM).The results show that the retrogression heating rate significantly affects the microstructures and mechanical properties of the alloys treated by retrogression and re-aging(RRA)process, and it is found that the medium rate(57℃/min)leads to the highest mechanical properties.The strengthening phases in the matrix are mainly the fine dispersed η′precipitates and GP zones,and the grain boundary precipitates are coarse and discontinuous η phases.

Microstructure characteristics and mechanical properties of rheocasting 7075 aluminum alloy

The microstructure characteristics and mechanical properties of 7075 aluminum alloy produced by a new rheoforming technique,under as-cast and optimized heat treatment conditions,were investigated.The present rheoforming combined the innovatively developed rheocasting process,named as ICSPC(inverted coneshaped pouring channel)process,and the existing HPDC(high pressure die casting)process.The experimental results show that the ICSPC can be used to prepare high quality semi-solid slurry for the subsequent die casting.Compared with conventional HPDC process,the ICSPC process can improve the microstructures and mechanical properties of the cast tensile samples.An optimized heat treatment results in significant improvement in ultimate tensile strength.However,the ductility of the samples,both under as-cast and optimized heat treatment conditions,are relatively poor.

The influence of gradient mismatches on mechanical properties and microstructure of 2219-T6 aluminum alloy VP-TIG joints

In this paper,6 mm thick 2219-T6 aluminum alloy was joined by means of variable polarity tungsten-arc welding( VP-TIG) and the influence of gradient mismatches on VP-TIG joints is investigated. The average tensile strength of the joints reduces 32%,53% and 59%,when the mismatch of the joint was 0. 635 mm,1. 44 mm,1. 83 mm,respectively.Incomplete penetration,additional bending moment( Ma) and decrease of effective load region area are considered to explain this phenomenon. The fracture location of tensile specimens occurred at the weld zone( WZ) close to partial melt zone( PMZ),corresponding to a sharp decline of microhardness from PMZ to WZ. The original position of fracture is found at weld toe,where incomplete penetration forms due to the introduction of gradient mismatches.

Effect of Samarium(Sm)Addition on Microstructure and Mechanical Properties of Al-5Cu Alloys

The purpose of this study is to investigate the influence of samarium addition on the microstructures and mechanical properties of Al-5Cu alloys. The microstructures were examined by optical microscopy, X-ray diffraction, scanning electron microscopy, energy diffraction spectroscopy and differential thermal analysis. It was found that Sm was capable significantly of affecting the microstructures of Al-5Cu alloys. When 0.4 wt% Sm was added into the alloy, the aspect ratio and the mean area of Al2Cu phase were 10.9 and 61.0 grn：. They were decreased by 31.5% and 43.3% when compared with unmodified alloy. Meanwhile, a kind of nano size strengthening Al2Sm phase was formed in Al-5Cu alloys. In addition, the differential thermal analysis results showed that Sm addition results in a decrease in the melting temperature of ct-Al and Al2Cu. And a good combination of yield strength （244.5 MPa）, ultimate tensile strength （269.4 MPa） and elongation （6.9%） was obtained when the Sm addition was 0.4 wt%. Compared with unmodified Al-5Cu alloys, they were increased by 37.6%, 35.2% and 21.1%, respectively.

Effect of Y content on microstructure and mechanical properties of 2519 aluminum alloy

The effects of yttrium(Y) content on precipitation hardening, elevated temperature mechanical properties and morphologies of 2519 aluminum alloy were investigated by means of microhardness test, tensile test, optical microscopy(OM), transmission electron microscopy(TEM) and scanning electron microscopy(SEM). The results show that the tensile strength increases from 485 MPa to 490 MPa by increasing Y content from 0 to 0.10%(mass fraction) at room temperature, and from 155 MPa to 205 MPa by increasing Y content from 0 to 0.20% at 300 ℃. The high strength of 2519 aluminum alloy is attributed to the high density of fine θ′ precipitates and intermetallic compound AlCuY with high thermal stability. Addition of Y above 0.20% in 2519 aluminum alloy may induce the decrease in the tensile strength both at room temperature (20 ℃) and 300 ℃.

Microstructure characteristics and mechanical properties of rheoformed wrought aluminum alloy 2024

The microstructure characteristics and mechanical properties of 2024 wrought aluminum alloy produced by a new rheoforming technique under as-cast and optimized heat treatment conditions were investigated. The present rheoforming combined the independently developed rheocasting process, named as LSPSF (low superheat pouring with a shear field) process, and the existing squeeze casting process. The experimental results show that LSPSF can be used to prepare sound semi-solid slurry within 25 s to fully meet the production rate of squeeze casting. The primary α(Al) presents in mean equivalent diameter of 69 μm and shape factor of 0.76, and features zero-entrapped eutectics. Compared with conventional squeeze casting, the present LSPSF rheoforming can improve the microstructures and mechanical properties. An optimized heat treatment results in substantial reduction of microsegregation and significant improvement of mechanical properties, such as yield strength of 321 MPa, ultimate tensile strength of 428 MPa and elongation of 12%.

Microstructure and mechanical properties of the welding joint filled with microalloying 5183 aluminum welding wires

In this study, 7A52 aluminum alloy sheets of 4 mm in thickness were welded by tungsten inert gas welding using microalloying welding wires containing traces of Zr and Er. The influence of rare earth elements Zr and Er on the microstructure and mechanical properties of the welded joints was analyzed by optical microscopy, energy dispersive X-ray spectroscopy, transmission electron microscopy, hardness testing, and tensile mechanical properties testing. Systematic analyses indicate that the addition of trace amounts of Er and Zr leads to the formation of fine Al3Er, Al3Zr, and Al3（Zr,Er） phases that favor significant grain refinement in the weld zone. Besides, the tensile strength and hardness of the welded joints were obviously improved with the addition of Er and Zr, as evidenced by the increase in tensile strength and elongation by 40 MPa and 1.4%, respectively, and by the welding coefficient of 73%.

Microstructure and mechanical properties of rheo-diecasted A390 alloy

The microstructure and mechanical properties of the rheo-diecasting(RDC) A390 alloy under as-cast and T6 heat treatment conditions were investigated.The results indicate that the RDC sample has fine and uniform microstructure throughout the sample under the as-cast condition,and the average size of primary Si spheroids is 20-30 μm.Meanwhile,the intermetallic compounds in RDC sample are reduced.Compared with the alloy produced by conventional liquid die-casting(LDC),RDC samples have improved tensile strength,ductility,hardness and wear resistance.It is also found that heat-treatment of the RDC A390 alloy under T6 condition,can substantially improve mechanical properties,with the tensile elongation more than 100% improvement.

Effect of rolling geometry on the mechanical properties, microstructure and recrystallization texture of Al–Mg–Si alloys

The effect of rolling geometry on mechanical properties, microstructure, and recrystallization texture of Al-Mg-Si alloys was studied by means of tensile tests, microstrucmral observations, and electron backscatter diffraction measurements. The results reveal that the elongation and the average plasticity strain ratio （r） values of the T4P （pre-aging plus natural aging）-treated alloy sheet with a rolling geome- try value between 1 and 3 are somewhat higher than those of the T4P-treated sheet with a rolling geometry value between 3 and 6. The deformation and recrystallization microstructures of the sheet with a rolling geometry value between 1 and 3 are more uniform than those of the sheet with a rolling geometry value between 3 and 6. The former also possesses somewhat higher surface quality. H {001 } 〈110〉 and Goss {110}〈001〉 orientations are the main recrystallization texture components for the former case, whereas the latter case only includes H {001 } 〈 110〉 orientation. Texture gradients are present in the two alloy sheets. Shear texture component F on the surface of the sheet with a rolling geometry value between 3 and 6 and its higher texture gradients have revealed that non-uniform deformation occurred during cold rolling. The effects of texture on the yield strength and r value were also discussed.

Effects of Ag on microstructure and mechanical properties of 2519 aluminum alloy

The effects of Ag on the microstructure and mechanical properties of 2519 aluminum alloy were investigated by means of tensile test, micro-hardness test, transmission electron microscope and scanning electron microscope. The results show that the addition of 0.3% (mass fraction) Ag accelerates 2519 aluminum alloy’s age-hardening, increases its peak hardness and reduces 4h of peak aged time at 180℃. The addition of 0.3%(mass fraction) Ag increses the tensile strength at room temperature and elevated temperature. This increment at room temperature and 200℃ is 24MPa and 78MPa, respectively. In contrast, the elongation of 2519 aluminum alloy is decreased with Ag addition. The increase of tensile strength of 2519 aluminum alloy with Ag addition is attributed to the high volume fraction of Ω phase.

Mechanical properties and microstructural evolution of rheocast A356 semi-solid slurry prepared by annular electromagnetic stirring

Nowadays,having an effective technique in preparing semi-solid slurries for rheocasting process seems to be an essential requirement.In this study,semi-solid slurry of A356 aluminum alloy was prepared by three-phase annular electromagnetic stirring(A-EMS)technique under different conditions.The effects of stirring current,pouring temperature and stirring time on microstructural evolution,mean particle size,shape factor and solid fraction were investigated.The rheocasting process was carried out by using a drop weight setup and to inject the prepared semi-solid slurry in optimal conditions into the step-die cavity.The filling behavior and mechanical properties of parts were studied.Microstructural evolution showed that the best semi-solid slurry which had fine spherical particles with the average size of~27μm and a shape factor of~0.8 was achieved at the stirring current of 70 A,melt pouring temperature of 670℃,and stirring time of 30 s.Under these conditions,the step-die cavity was completely filled at die preheating temperature of 470℃.The hardness increases by decreasing step thickness as well as die preheating temperature.Moreover,the tensile properties are improved at lower die preheating temperatures.The fracture surface,which consists of a complex topography,indicates a typical ductile fracture.