Microstructure Of Aluminum Alloy Research Articles

Primary phase transformation mechanism in a hypereutectic Al-Ce alloy during rapid solidification

Cooling rate plays an important role in determining the microstructure in as-cast aluminum alloys. To obtain a cooling rate gradient, a wedge Cu mould was selected. Here, we found a transition from hypereutectic to hypoeutectic microstructures in a hypereutectic Al-Ce alloy during rapid solidification. There was a distinct interface at a cooling rate of 1598 K/s. When the cooling rate was lower than 1598 K/s, the microstructures were composed of primary Al11Ce3 phases and Al/Al11Ce3 eutectic colonies. As the cooling rate was higher than 1598 K/s, the primary Al11Ce3 phases transformed into α-Al. Compared with the α-Al, the nucleation of Al11Ce3 phases was more favorable because of the lower nucleation energy. The growth rate of α-Al was higher than that of Al11Ce3 phases as the undercooling was larger than 182 K. Primary phase transformation mechanism in the hypereutectic Al-Ce alloy was controlled by nucleation and growth of α-Al and Al11Ce3 phases.

Welding and galvanic coupling effects on the electrochemical activity of dissimilar AA2050 and AA7050 aluminum alloys welded by Friction Stir Welding (FSW)

In this work, the effects of friction stir welding (FSW) on the microstructure and electrochemical activities of dissimilar AA2050 and AA7050 aluminum alloys have been investigated. Local electrochemical tests supported by surface analytical characterization were used to study the local electrochemical activities developed along the weld zones of the dissimilar alloys. The investigation was carried out on the cross-section of the welded Al alloys. The results showed that the friction stir welding (FSW) of the dissimilar alloys affected the microstructure and the electrochemical behavior of the different regions (HAZ, TMAZ, SZ) formed by the welding process. Scanning vibrating electrode technique (SVET) and micropotentiometry by using an ion-selective microelectrode showed that TMAZ was the zone with the highest electrochemical activity. This zone corresponded to the transition region between the two welded alloys. The high electrochemical activity observed in this region was associated with the effect of welding on the microstructure and, also, with the galvanic coupling between the two alloys, where the alloy AA7050 acted as an anode and the AA2050 as a cathode. Preferential corrosion attack on the AA7050 alloy was also evident.

Effect of Er, Si, Hf and Nb Additives on the Thermal Stability of Microstructure, Electrical Resistivity and Microhardness of Fine-Grained Aluminum Alloys of Al-0.25%Zr.

The conductor aluminum alloys of Al-0.25wt.%Zr alloyed additionally with X = Er, Si, Hf and Nb were the objects of our investigations. The fine-grained microstructure in the alloys was formed via equal channel angular pressing and rotary swaging. The thermal stability of the microstructure, specific electrical resistivity and microhardness of the novel conductor aluminum alloys were investigated. The mechanisms of nucleation of the Al3(Zr, X) secondary particles during annealing the fine-grained aluminum alloys were determined using the Jones-Mehl-Avrami-Kolmogorov equation. Using the Zener equation, the dependencies of the average secondary particle sizes on the annealing time were obtained on the base of the analysis of the data on the grain growth in the aluminum alloys. The secondary particle nucleation during long-time low-temperature annealing (300 °C, 1000 h) was shown to go preferentially at the cores of the lattice dislocations. The Al-0.25%Zr-0.25%Er-0.20%Hf-0.15%Si alloy subjected to long-time annealing at 300 °C has the optimal combination of microhardness and electrical conductivity (59.8%IACS, Hv = 480 ± 15 MPa).

A brief review on pre- and post-weld treatment of various grades of aluminium alloys

In the present paper, different types of pre- and post-weld treatments performed on aluminium alloys have been reviewed. Aluminium is the second most widely produced material after steel. Aluminium alloys can be welded using fusion welding techniques but they distort the weldments’ microstructure and the welds are prone to oxidation, porosity and cracking. Therefore, modern welding techniques like laser beam welding, electron beam welding and friction stir welding are now performed on aluminium alloys. Further, treatments like reinforcement, pre-weld and post-weld heat treatment and cryogenic treatment have also been performed by researchers and discussed in the paper. The application of various treatments has significantly improved the aluminium alloy weldments’ properties especially cryogenic treatment. The effect of preheat and cryogenic treatment on microstructure and mechanical properties of aluminium alloys’ weldments has not been researched properly and they require more attention of researchers.

Electrochemical corrosion behavior of 6061 Al alloy under high rotating speed submerged friction stir processing

In this study, we report the high rotating speed submerged friction stir processing (HRS-SFSP) designed to modify 6061 Al alloy to improve its corrosion resistance in saltwater. The effect of this processing technology on the microstructure and corrosion behavior of aluminum alloy was studied. The results show that the grain size of Al alloy after HRS-SFSP was refined from 50.8 µm is refined to 3.21 µm. In addition, compared with the low rotation speed (1800 r/min), a higher proportion of high-angle grain boundaries (77.1 %) formed when the rotation speed was 3600 r/min, which effectively reduced the defect density. At the same time, recrystallization in a large area lowered the energy storage in the grain, which further alleviates the corrosion. In addition, the second phase dominated by Mg2Si was fine and uniformly distributed, which also reduced the galvanic corrosion tendency. Therefore, high corrosion resistance was obtained using HRS-SFSP. On the other hand, continuously increasing the rotation speed coarsened the grains and the second phase,which decreased the corrosion resistance.

Phase Composition and Microstructure of High Strength AA6xxx Aluminium Alloys with Nickel Additions

Phase Composition and Microstructure of High Strength AA6xxx Aluminium Alloys with Nickel Additions

Refining microstructure of medium-thick AA2219 aluminium alloy welded joint by ultrasonic frequency double-pulsed arc

The increasing demand for achieving high-efficiency and high-quality medium-thick aluminium alloy welded structures, especially for large scale aerospace components, presents an urgent challenge to the conventional TIG arc welding process. This work proposed a novel double-pulsed variable polarity tungsten inert gas (DP-VPTIG) arc, in which the variable polarity square wave current was simultaneously modulated into ultrasonic frequency (20–80 kHz) and low frequency (0.5–10 Hz) pulses. Full penetration welds of 6 mm thick AA2219 aluminum alloy were successfully obtained by using this process. The microstructure and mechanical properties of the weld produced by DP-VPTIG arc were investigated, taking the conventional VPTIG arc as a comparative study. Results show that the microstructure of weld zone by DP-VPTIG arc showed an alternating distribution of fine equiaxed grain band and slightly coarse equiaxed grain band. Compared to VPTIG arc, the grain structure was effectively refined in the weld zone with DP-VPTIG arc, showing a significant reduction of average grain size by 51.2% along transverse section and 61.3% along longitudinal section. The morphology of α-Al+θ-CuAl2 eutectics transformed from continuously distributed netlike shape to separately distributed granular shape, and segregation of Cu solute element was obviously improved. The average microhardness of weld zone was increased by about 8.7% and 5.6% along transverse section and along longitudinal section. The tensile properties of ultimate tensile strength, yield strength and elongation were increased by 6.6%, 10.6% and 20.5%, respectively. The results provide a valuable basis for improving welding efficiency and joint quality through a hybrid pulsed arc.

Microstructure and microhardness of aluminium alloy with underwater and in-air wire-feed laser deposition

Microstructure and microhardness of aluminium alloy with underwater and in-air wire-feed laser deposition

Effect of rolling deformation and passes on microstructure and mechanical properties of 7075 aluminum alloy

The research on Al–Zn–Mg–Cu alloys mainly focuses on the effects of solution aging and strain rate on the microstructure and properties of the alloy, as well as the flow stress behavior of the alloy. There are few studies on the effects of hot rolling deformation and reduction pass on the microstructure and properties of aluminum alloy. The dislocation density of alloy is affected by changing the rolling deformation, and post-heat treatment improves fine grains segregation and break coarse second phases. The alloys comprehensive mechanical properties are improved by controlling the recrystallization fraction and size. Different shape variable rolling and different passes, optical microscope (OM), field emission scanning electron microscope (SEM) with energy dispersive spectrometers (EDS), X-ray diffractometer (XRD), microhardness tester, and other methods were used to characterize the samples, and simulation of the rolling process analyzed by Deform-3D software. The effects of hot rolling deformation and deformation pass on microstructure and properties of aluminum alloy were also studied. The results show that dynamic recrystallization was beneficial to grain refinement when deformation increases to 40%. The coarse second phase was broken and refined into chains and partially spheroidized to dissolve in the matrix under large deformation. Dislocation density decreased after solution treatment when deformation was less than 80%, and increased after large deformation was 80%. The equivalent strain obtained by numerical simulations increases with the increase of deformation. The maximum equivalent strain was on both sides of the rolling surface, and this area was the most prone to crack in rolling. When the increase of the shape variable, the recrystallization volume fraction increased, and the grain size decreased.

Mechanism of grain refinement in Al-Cu alloy by adding trace La and Al-5Ti-1B

<sec>Grain refinement of aluminium alloys can not only reduce the defects (such as segregation and hot tearing) but also improve the mechanical properties. Adding Al-5Ti-1B master alloy to the melt has become a common method to refine the solidification microstructure of aluminium alloys. A lot of researches have been carried out to uncover the grain refining mechanisms as well as to show the microstructure formation under the effect of grain refiner. These researches demonstrated that the grain refining efficiency is closely related to the number density of TiB<sub>2</sub> particles as well as the solute Ti concentration in the melt. However, there exist still problems to be resolved, such as the limited grain refinement potency of Al-5Ti-1B master alloy. Recently, the addition of trace La to the melt has attracted much attention to control the microstructure of aluminium alloys. The Al-Cu alloys are widely applied to the automobile and aerospace fields due to their high strength, good ductility and high temperature properties. It has been reported that Cu can segregate to Al/TiB<sub>2</sub> interface in the Al-Cu melt inoculated with Al-5Ti-1B master alloy. But the effect of Cu segregation on the grain refinement result is not clear yet. Meanwhile, whether the grain refinement effect of Al-5Ti-1B master alloy on Al-Cu alloy can be improved by the addition of trace La has not been reported.</sec><sec>Solidification experiments are carried out for Al-2Cu alloy with the addition of Al-5Ti-1B master alloy+ trace La. The synergistic effect of trace La and Al-5Ti-1B on the solidification microstructure of Al-2Cu alloy is investigated. It is found that trace La can effectively enhance the refinement result of Al-2Cu alloy and further diminish the nucleation undercooling. Experimental and calculated results demonstrate that solute Cu segregates to the Al/TiB<sub>2</sub> interface and thus increases the interatomic spacing mismatch between Ti (0001) plane of the TiB<sub>2</sub> particles and the interfacial monolayer, while La segregation reduces the interatomic spacing mismatch. The trace La addition reduces the interfacial energy between <i>α</i>-Al and TiB<sub>2</sub> particles, improves the potency of TiB<sub>2</sub> particles to nucleate <i>α</i>-Al, and thus enhances the grain refinement result of Al-5Ti-1B master alloy.</sec>

Effect of MGZN2 addition on the sintering density, microstructure and hardness of aluminum alloys prepared by powder metallurgy method

Effect of MGZN2 addition on the sintering density, microstructure and hardness of aluminum alloys prepared by powder metallurgy method

A critical review on microstructure and hardness of aluminum alloy 6061 joints obtained by friction stir welding-past, present, and its prospects

A critical review on microstructure and hardness of aluminum alloy 6061 joints obtained by friction stir welding-past, present, and its prospects

Microstructure and Fatigue Properties of Al2024-RAM2 Aluminum Alloy Obtained by Laser Powder Bed Fusion

The wrought 2024 aluminum alloy is an established aluminum alloy with copper as the primary alloying element. Due to its high strength and fatigue resistance, it is widely used for aircraft primary structures. Development of the AM counterpart of this high-strength alloy starting from gas atomized powder has been challenged by its tendency to hot tearing during solidification thus compromising mechanical properties. Recently, the innovation by Elementum 3D made the 2024 alloy compatible with the Laser Powder Bed Fusion technology (L-PBF). The key is a patented production process of reactive additive manufacturing (RAM), which utilizes exothermic chemical reactions to synthesize product materials during the additive process to improve printability while achieving mechanical properties comparable to those of a conventionally produced alloy.This contribution examines the Al2024-RAM2 alloy recently qualified for industrial production by the service company BEAM IT (Fornovo Taro, Italy). The powder was processed in a SLM 280 HL Twin system (SLM Solutions GmbH, DE) to fabricate specimens for fatigue testing which then underwent a solution-plus-aging heat treatment (T6). Specimens oriented in three different directions with respect to the build direction were left in the as-built surface state and used for the characterization of microstructure and surface quality. Fatigue data obtained under high cycle fatigue loading conditions are presented and discussed in terms of directional effect and surface integrity (as-built vs. polished surfaces).

Quantitative assessment of inhomogeneity of dendritic structure of aluminum alloys based on their microstructural analysis

The microstructure of various aluminum alloys is studied by measuring the secondary dendrite arm spacings. To process the experimental data, the mathematical apparatus of the lognormal distribution is used. It is shown that this approach provides an effective convolution of experimental information for the calculation estimate of the mesoscale inhomogeneity of secondary dendrite arm spacing.

The influence of the modifying elements on the microstructure, mechanical, and deformation properties of aluminum alloys

In the current work, the standard A242 aluminum cast alloy is modified using the stir casting method with titanium (Ti) (0.5% wt.) and boron (B) (0.1% wt.) modifiers. Polarized optical and scanning electron microscopy were utilized to examine the A242 base microstructure, and A242 + TiB modified alloys; the results revealed that the modified A242 + TiB alloy was refined by 13.5 times more than the as-cast alloy. The mechanical properties were investigated experimentally using compression test in addition to the hardness test; the results revealed that the ultimate compressive strength of the A242 + TiB modified alloy was increased by 9.0% more than those of the A242 standard alloy. Moreover, the yield stress was enhanced by 40% at room temperature and 20% at 250 °C. The dynamic properties were studied using a free vibration impact test to study the modifiers’ effect on the dynamic behavior. The grain refinement notably impacted the damping capacity; due to the as-cast inhomogeneity, the conventional alloy A242 exhibited a greater FRF than the modified alloy A242 + TiB. The modified alloy displayed fewer resonance peaks due to grain refinement and excellent intermetallic phase distribution. The simulation process of the investigated alloys was performed using ABAQUS finite element software to predict the deformation behavior under different temperatures. The FE results showed that the modified alloy was more resistant to deformation by 9.1% than the reference alloy, A242, at room temperature and 7.6% at 250 °C, which agreed with the experimental findings.

Refinement of the Magnesium-Aluminium Alloy Microstructure with Zirconium.

The magnesium-aluminium alloy AZ91 was inoculated with zirconium to refine the microstructure. Six different concentrations of zirconium content were tested, ranging from 0.1 to 0.6 wt %, and compared to the baseline AZ91 alloy without modification. Melted metal was poured into a preheated ceramic mould and the temperature was measured and recorded during the solidification. The derivative and thermal analysis (DTA) was performed to compare the crystallisation dynamics. Formed microstructure was analysed using an optical microscope, scanning electron microscopy (SEM-EDX) and energy dispersive X-ray spectrometry (XRD). The chemical composition was measured using an arc spectrometer. The time of solidification was shortened for the samples with a concentration of zirconium 0.3 wt % and the microstructure was refined. The level of grain refinement remained below 10% and the grain shape was changed to more spherical shapes. Both the primary magnesium and eutectic phases were modified. However, at a low concentration of zirconium (0.1 and 0.2 wt %), the primary grain size was increased. Therefore, the optimal zirconium concentration was 0.3 wt %. Larger concentrations (0.4 to 0.6 wt %) did not provide any additional benefit. Theoretical analysis showed that some Al3Zr intermetallic phases can form, which was confirmed on the derivate curve of the thermal analysis, and SEM-EDS and XRD analyses.

Effect of CMT Welding Heat Input on Microstructure and Properties of 2A14 Aluminum Alloy Joint

Cold metal transfer (CMT) welding is an attractive welding technology for thin sheet aluminum alloys because of its low heat input, arc stability and spatter-free behavior during the welding process. The present research is mainly concerned with the effect of different heat input on microstructure and mechanical properties of CMT welding 2A14 aluminum alloy in 3 mm thickness. The results indicate that a welded joint with good quality can be achieved when the welding current is 105 A and welding speed is 8 mm/s. The weld width and porosity gradually increase along with the constantly increasing welding heat input. The center of the welded joint consists of a large number of fine equiaxed dendrites, and the gray matrix is uniformly distributed accompanied by a large number of dots and blocks as a white second phase, corresponding to the composition of the Al2Cu phase. The microhardness of welded joints under different welding heat input maintains relative stability and presents a certain softening degree; the base material is the highest, followed by the heat-affected zone.

Measurement of Air Entrainment and its Effect on the Microstructure and Mechanical Properties of a A356 Aluminum Alloy

Measurement of Air Entrainment and its Effect on the Microstructure and Mechanical Properties of a A356 Aluminum Alloy

Effect of Single and Double Pulse MIG Welding Process Parameters on Microstructure and Properties of Aluminium Alloy

Lightweight aluminium alloys are widely used in many industries due to their advantageous mechanical properties. As welding is a popular method for joining aluminium alloy sheets, it is important to understand how the welding process affects the alloy’s performance. Here, we investigated the influence of various operating parameters during pulsed metal inert gas (MIG) welding of thin aluminium alloy plates on the input energy and metallurgical microstructure of the weld. A series of welding tests were performed using surface welding of AA6061 aluminium alloy plates under conditions of a single strong-pulse, single weak-pulse, or double pulse. The morphology, metallurgical structure, and hardness of the welds produced using the different welding parameters were then examined. We observed that increasing the welding speed and the arc duration of low-energy pulses can reduce the heat input. Lower heat input is advantageous as it results in a higher cooling rate of the welding pool and a smaller average grain size of the weld structure. In addition, increasing the welding speed increased the hardness of the weld. Double pulsed MIG welding showed the best overall weld performance and is recommended for improving the quality of aluminium alloy bonding.

Microstructure and Mechanical Properties of ZL205A Aluminum Alloy Produced by Squeeze Casting after Heat Treatment

In this paper, ZL205A (AlCu5Mn alloy) castings were prepared by squeeze casting. The effects of solution and ageing treatment on the microstructure and mechanical properties of ZL205A castings were studied by metallography, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and mechanical properties tests. The results showed that most of the θ(Al2Cu) and T(Al12CuMn2) phases in squeeze-cast ZL205A dissolved into the α(Al) matrix after solution treatment for 15 h. The fine precipitates gradually increased with the ageing time. The ultimate tensile strength of the specimen aged for 6 h was the highest of 467 MPa and the elongation was up to 15.1%, showing good comprehensive mechanical properties.