Precipitation Of Mg2Si Research Articles

A novel Al-Zn-Mg-Cu-Si-Zr-Er alloy fabricated by laser powder bed fusion

A novel Al-Zn-Mg-Cu-Si-Zr-Er as-printed alloy with a tensile strength of 450 MPa was successfully prepared by laser powder bed fusion (LPBF). Solidification cracks were effectively suppressed by the synergistic effect of Si, Zr and rare earth Er. Many cellular eutectic structures composed of α-Al, Mg2Si and Al2CuMg phases were observed in the alloy, with Al3(Er, Zr) and MgZn2 as the fine precipitates inside the cells. In addition, twins were observed for the first time in Al-Zn-Mg-Cu alloy prepared by LPBF due to the high rapid solidification inherent to LPBF. Twin boundaries acted as nucleation point for the precipitation of Mg2Si and Al2CuMg, which is called “twin nucleation” theory. This study could provide a scientific theoretical reference and new approach for the preparation of high-strength aluminum alloys by LPBF.

Effect of Two-Step Solution Treatments on the Microstructure and Mechanical Properties of B357 Aluminum Alloy

AbstractThis study investigates the effect of two-step solution treatments and aging times on the microstructure and mechanical properties of B357 Al–Si alloy, part of the most widely used cast aluminum alloy. Three sets of artificial aging heat treatments were conducted on the tensile samples prepared from B357 alloy produced by low-pressure die casting. Firstly, the conventional artificial aging heat treatment (T6) was carried out by solutionizing the tensile samples at 543 °C for 8.5 h, water quenching at 60 °C, and then artificially aging for 8.5 h at 160 °C. In the two-step solution treatment, the samples were solutionized at 400, 440, 480, and 520 °C for 4 h and then solutionized at 543 °C for 8.5 h and water quenched to 60 °C and then artificially aged for 8.5 h at 160 °C. Thirdly, the samples were solutionized at 480 °C for 4 h, solutionized at 543 °C for 8.5 h, water quenched to 60 °C, and artificially aged for 3–192 h. Despite different solutioning and aging processes, no significant differences were observed in the microstructures of the samples. Si particle coarsening was observed with increasing solution temperature (400–520 °C) and aging times (3–192 h). Si-containing dispersoids and dispersoid-free zones (DFZ) were observed in the primary-α matrix. While DFZ width increased with temperature and aging, dispersoid zones in primary-α dendrites significantly decreased. Differential Scanning Calorimetry (DSC) analysis shows that two-step solution treatment in B357 alloy increases β′ precipitates for Mg2Si precipitation strengthening. The two-step solutionized and aged sample showed the best combination of strength and ductility among all aged samples. B357 alloy exhibited the highest yield and tensile strength (309.7, 366.1 MPa) with 6% elongation for two-step solutionizing and 48 h aging. All aged B357 alloys showed ductile fracture as the primary fracture mode. However, brittle fractured Si particles were observed on the fracture surfaces.

Manipulating microstructure and mechanical properties of laser powder bed fusion processed hypo-eutectic Al-13.3Mg2Si alloy via annealing

The annealing of a hypo-eutectic Al-13.3 wt%Mg2Si alloy processed by laser powder bed fusion (LPBF) was carried out for the correlation between the evolution of cellular eutectic Mg2Si and mechanical properties. The LPBFed Al-13.3Mg2Si was featured by cellular eutectic Mg2Si and free Mg2Si inside the α-Al matrix. Under the annealed conditions (200 ºC ∼ 450 ºC), the metastable cellular structures consisted of eutectic Mg2Si were gradually transferred to spherical free Mg2Si and eventually to stable polygon-like Mg2Si, thus leading to a decrease in tensile strength caused by the weakening of cellular boundary strengthening and dispersion strengthening. Moreover, over-annealing (>350 ºC) resulted in a drastic reduction in the ductility due to the formation of coarse polygon-like Mg2Si. The superior strength-ductility synergy (i.e. ultimate tensile strength (UTS) of 506 MPa and elongation (El) of 6%) has been obtained after annealing at 200 ºC for 6 h. The mechanism for the property improvement can be mainly attributed to the precipitation of partial cellular eutectic Mg2Si. The results demonstrate that it is possible to expand the scope of properties of LPBFed Al alloys through manipulating the metastable microstructures via annealing.

Tensile behavior of diffusion bonded AA6061 - AA6061 with variation in cooling method

Hot isostatically pressed AA6061 cladding is an important structural component of the high performance, Zr-laminated U-10Mo monolithic fuel system for the application in research and test reactors. In this study, the mechanical behavior of two diffusion bonded aluminum alloy, AA6061, was examined using tensile testing. Solid-to-solid diffusion bonding between two pieces of AA6061 was performed by isothermal annealing at 560 °C for 1.5 h, and diffusion couples were subsequently cooled via three different cooling methods: furnace cooling, air cooling, and water quenching. Dog-bone shaped tensile specimens, with 10 mm in gauge length (with diffusion bonded interface in the middle), and 1.5 × 1.5 mm2 gauge cross-sections, were fabricated from the diffusion bonded AA6061 by electro-discharge machining. Yield strength (% EL at failure) of furnace cooled, air cooled and water quenched tensile specimens determined was 82–89 MPa (10–30%), 112–116 MPa (10–14%), and 149–164 MPa (10–17%), respectively. This variation in mechanical behavior was examined with cooling-rate dependent, concentrated precipitation of Mg2Si at the diffusion bonded interface, with due respect for mechanical properties of the AA6061 alloy that inherently vary as a function of cooling rate from 560 °C. Finite element analysis using ABAQUS was employed to augment experimental findings with the appropriate microstructural constituents and alloy properties. Results suggest that the strength is dominated by matrix/bulk properties of AA6061, while ductility is strongly influenced by the cooling method dependent presence of Mg2Si precipitates at the interface.

Morphological modification of Mg2Si phase and strengthening mechanism in Mg2Si/Al composites by Eu addition and T6 heat treatment

In order to improve mechanical properties of Mg2Si/Al composites, Eu element was added to modify Mg2Si morphology, and T6 heat treatment was used to control Mg2Si morphology and precipitate strengthening phase. Microstructure and morphology of Mg2Si were observed by synchrotron X-ray tomography and TEM, and first-principles calculations were also performed to testify the effect of Eu modification. Results show that the size of primary Mg2Si particles decreases and eutectic Mg2Si phase transforms from lamellar to fibrous by Eu addition. After heat treatment, sharp angles of primary Mg2Si particles passivate, and eutectic Mg2Si dissolves and appears to be short dot-like. Meanwhile, nano-sized β" phase precipitates in the matrix. For morphology of Mg2Si with Eu modification, TEM results show that Eu impedes the growing of Mg2Si, which is verified by first-principles calculations that Eu atom preferentially adsorbs on Mg2Si {100} facet. The adsorption and suppression growing of Mg2Si transform the morphology of Mg2Si and thus improve the elongation. UTS and elongation of the heat-treated Eu modified composites are 281 MPa and 8.4%, which improved 81% and 200% compared to the as-cast Al-15%Mg2Si composite. The strengthening mechanism mainly results from precipitation strengthening of nano-sized β" precipitates in the heat-treated composite.

Influence of powder layer thickness on microstructure and T5 heat treatability of F357 alloy fabricated by laser powder bed fusion process

Laser powder bed fusion (LPBF) is one of the most widely used additive manufacturing (AM) methods to produce metal parts with new functionalities, but it still suffers from a low built rate. Increasing the powder layer thickness is an efficient way to augment LPBF productivity. The objective of this study is to investigate the influence of the powder layer thickness during the LPBF of F357 alloy on the microstructure and age-hardening response during T5 heat treatment. Scanning electron microscope (SEM) and transmission electron microscope (TEM) observations show that microstructure differences are negligible between samples printed at 30 µm and 50 µm layer thicknesses in the as-built condition. Samples built with both layer thicknesses and subjected to T5 heat treatments at 150 °C, 160 °C, and 170 °C also show similar microstructures and their α-Al cells contain large Si precipitates and small Si clusters and no β’’-Mg2Si precipitates. Therefore, β’’-Mg2Si precipitation hardening is not the dominant mechanism, and strengthening appears to be mainly due to the small Si clusters. With the help of the Johnson-Mehl-Avrami (JMA) model, the activation energy of the precipitation process of the samples built at 30 and 50 µm layer thicknesses is calculated to be 142 kJ/mol and 139 kJ/mol, respectively. These comparable values suggest a similar evolution of the precipitation hardening for both layer thicknesses, which is consistent with the observed microstructures. Consequently, the production efficiency of LPBF-printed F357 alloys can be enhanced by using higher layer thickness and the T5 heat treatment.

Evaluation of age-hardening time on the mechanical behavior of Al-Mg-Si (Al 6063) alloy composites reinforced with alumina particles

This research attempts to evaluate the effects of age-hardening on the mechanical behavior of aluminum (6063) alloy reinforced with alumina (Al2O3) particles. Aluminum (6063)/Al2O3 composites containing 0, 5, 7, 9 and 10 wt% Al2O3 particles respectively were fabricated using double stir casting technique and representative samples from each composition were subjected to age-hardening treatment at 180 °C for 60 min, 120 min and 180 min respectively. The microstructures were evaluated using SEM while fracture toughness and tensile properties were used to evaluate the mechanical behavior of both the as-cast composites and their age-hardened counterparts. The microstructure evaluation reveals formation of coherent precipitates of Mg2Si evenly distributed in the age-hardened composites. Significant improvement in tensile strength values of 129.8, 88.6, 90.6, 137.9 and 170.6 MPa were obtained for the age-hardened composites compared to their as-cast composites with 42.2, 72.9, 81.2, 80.84 and 71.5 MPa across the series respectively. Similar trend was observed for fracture toughness with KIC values of 7.5, 5.8, 4.5, 7.8 and 9.6 MPam1/2 for age-hardened composites compared with 4.68, 4.64, 4.07, 4.06 and 3.59 MPam1/2 obtained for their as-cast composites. Age-hardening time of 180 min impart better tensile strength and fracture toughness.

The microstructure and texture evolution of Mg-5Sn-1Si-0.8Y alloy during the reciprocating extrusion process (REP)

In this paper, the microstructure and texture evolution of Mg-5Sn-1Si-0.8Y alloy fabricated by reciprocating extrusion process (REP) at 340 ℃ for 2–8 passes is characterized by optical microscopy (OM), Scanning Electron Microscope (SEM) and Electron Backscatter Diffraction (EBSD).The results show that the microstructure was refined significantly, dynamic recrystallization (DRX), fragmentation of the second Mg2Si phase and precipitation of the Mg2Sn phase occurred during REP. With the increase of the REP passes, the fraction of low angle grain boundaries (LAGBs) showed a decreasing trend and the secondary phases distribution became more and more homogeneous and the degree of DRX was increased. At the same time, the initial extruded fiber basal texture was gradually weakened and became random as the REP passes increases. The hardness of the alloy also shown an increasing trend with the increase of REP passes. The grain refinement mechanism, texture evolution and increase of hardness were mainly related to the dynamic recrystallization and the particle stimulation nucleation (PSN) effect of the second phases.

Effects of solution aging on mechanical and microstructures properties of Al6092/SiCp/β-eucryptite composites

This paper studied Al6092/SiCp/β-LiAlSiO4 particle-reinforced aluminum matrix composites as the main object. Different solution aging treatment processes were selected to analyze the microstructure and mechanical properties of the specimens. The effects of solution aging on the microstructure, precipitation phases, and dislocations of the composites were revealed. The results showed that the solution aging treatment improved the stiffness and strength of Al6092/SiCp/β-LiAlSiO4 composites. On the one hand, solution aging promoted the generation of high dislocation density zones and Mg2Si precipitation phases in the samples, which increased the stress required for plastic deformation of the composites. In addition, the high modulus property of micron-sized SiCp can spontaneously carry loads, and the introduction of β-LiAlSiO4 promotes the dispersion of the reinforcing phase. In conclusion, the solution aging treatment and the particle-reinforced phase can jointly improve the deformation resistance of Al6092.

Characterization of the solidification behavior, microstructure and mechanical properties of aluminum alloy 6063 with samarium addition

The present work investigates the effects of Samarium (Sm) addition on the performance of 6063 Aluminum alloy. The investigation includes aspects related to the solidification behavior, the microstructure and the mechanical properties for the reference alloy in addition to four modified alloys containing 0.1, 0.3, 0.5 and 1.0 wt% Sm. The reactions corresponding to the formation of α-Al, Al13Fe4, α-AlFeSi and Mg2Si are identified through thermal analysis of the reference alloy. The modified alloys experience similar reactions during solidification that, however, occur at slightly different temperatures, implying the modification of the forming phases due to Sm addition. Optical microscopic examination reveals 37 % grain refinement for the modified alloys due to the Sm addition up to 0.5 wt%. Sm addition influences also the Fe-bearing precipitates, causing the formation of granular Al-Sm-Si-Fe-Mg due to the addition of 0.1 wt% Sm. Samarium addition beyond 0.1 wt% induces the formation of Fe-free Al-Sm-Si-Mg intermetallics, having sharp plate-like and zigzag morphology, in addition to Sm-free Al-Fe-Si precipitates. The best mechanical performance, in the T6 condition, is achieved by the (AA6063 + 0.1 wt% Sm) alloy, attaining an increase of 38 % in the hardness and 11 % in the yield strength, in comparison to the unmodified alloy. The significant strengthening of the 0.1 wt% Sm modified alloy in the T6 condition suggests a promoted precipitation of Mg2Si during solidification due to the Sm addition.

Effect of Ultrasonic-Assisted Modification Treatment on the Microstructure and Properties of A356 Alloy.

Ultrasonic treatment was applied to an A356 aluminum melt with different modifiers, and the effects of ultrasonic treatment on the structure and properties of the A356 alloy were studied. The results showed that α-Al was effectively refined with different ultrasonic modification treatments. In particular, ultrasonic treatment showed the most obvious refinement with macroscopic grains of unmodified alloy and optimized the refinement of secondary dendrite arm spacings in the Sr/Ce synergistic alloys. The eutectic Si of the unmodified A356 alloy had no obvious change after the ultrasonic treatment, but the branch diameter of the eutectic Si reduced in the Sr and Sr/Ce modification alloys after the ultrasonic treatment. The ultrasonic treatment significantly improved the ultimate tensile strength and elongation of the as-cast A356 alloy with the unmodified material, which was due to refinement of the α-Al grains by the ultrasonic treatment. After the T6 heat treatment, the ultimate tensile strength values of the alloys showed no obvious change due to the ultrasonic treatment, but the plasticity of the alloy was significantly improved. Mg2Si precipitation was the dominant strengthening mechanism during the T6 heat treatment, while the plasticity was determined by the size and distribution of the eutectic Si. Acoustic cavitation caused by the ultrasound-activated impurities and the induced heterogeneous nucleation and supercooled nucleation in the groove melt was the main cause of the α-Al refinement, the eutectic Si modification and the improvement in the mechanical properties.

Correlation between Interface Microstructure and Bond Strength of Al6061/Al6061 HIP-Bonded Plates for Fuel Cladding Application

The effects of hot isostatic pressing (HIP) processing parameters on microstructure and bond strength of Al6061/Al6061 plate interfaces were systemically investigated at the micro- and nanoscale. The HIP bonding of the two aluminum plates was performed at four temperatures: 350°C, 400°C, 450°C, and 560°C. The results reveal the formation of micron scaled Mg2Si precipitate and uniform nano scaled Mg2Al2O5 oxide at the interface. The formation of Mg2Al2O5 is closely associated with the fast bulk diffusion of Mg from the Al matrix to the amorphous Al2O3/Al interface and subsequent reaction between Mg and Al2O3. The highest and lowest bond strengths were observed in samples HIP bonded at 450°C and 350°C, respectively.

Regulative effect of Mg/Si ratio on microstructure evolution and mechanical properties of cast Al-Li-Mg-Si alloys

The effect of the Mg/Si ratio of Al-2.5Li-1Cu-0.8Mg-0.8Si, Al-2.5Li-1Cu-1.6Mg-0.8Si, and Al-2.5Li-1Cu-2.4Mg-0.8Si alloys on the microstructure evolution and mechanical properties was investigated. The results show that the primary phases and their morphologies in the as-cast alloys are found to vary with the Mg/Si ratio. The improvement of Mg/Si ratio of as-cast alloys promotes the formation of Mg2Si primary phase at the expense of the AlLiSi primary phase. Moreover, a tiny amount of TB-Al7.5Cu4Li phase transforms into S-Al2CuMg phase with the increase of Mg content. In addition, the increase of Mg/Si ratio also causes the Cu-rich intergranular phase distributed along crystal boundary to Si-rich intergranular phase. After ageing treatment, the precipitation sequence as a function of Mg/Si ratio is as follows: δ/δ′+AlLiSi (Mg/Si is ∼1) → δ/δ′+β′-Mg2Si+AlLiSi (Mg/Si is ∼2) → δ/δ′+β′-Mg2Si (Mg/Si is ∼3). A good combination of strength and ductility can be obtained in Al-2.5Li-1Cu-2.4Mg-0.8Si alloy after solution and ageing. The rod-like β′-Mg2Si precipitate has a positive influence on the comprehensive mechanical properties of the alloy.

Coarsening behavior of Mg2Si precipitates during post homogenization cooling process in Al-Mg-Si alloy

The temperature and time dependence of the radii of Mg2Si precipitates in 6082 Al alloy under different post-homogenization cooling rates over a wide range of 32–120,000 °C/h were investigated by scanning and transmission electron microscopy. The equivalent radius of the Mg2Si precipitate decreased from 488 to 65 nm, associated with an increase in the cooling rate. The precipitating phase is primarily equilibrium β‐Mg2Si, as inferred from differential scanning calorimetry and X-ray diffraction. With the increasing cooling rate, the hardness of the alloy after T5 heat treatment initially increased and then plateaued. The critical cooling rate was identified to be 760 °C/h. A new thermodynamic particle coarsening model was designed to predict the evolution of particle size during the cooling process, and it presented appropriate agreement with the experimental data. This model can be applied to optimize alloys after the homogenization cooling process to ensure low deformation resistance, improve extrudability, and achieve maximum age-hardening effect in subsequent heat treatments.

On the extraordinary low quench sensitivity of an AlZnMg alloy

The scope of this work was to investigate the quench sensitivity of a high-purity wrought aluminum alloy Al6Zn0.75 Mg (in this work called 7003pure). This is compared to a similar alloy with the additions of Fe, Si, and Zr at a sum less than 0.3 at.% (in this work called 7003Fe,Si,Zr). Differential scanning calorimetry (DSC) was used for an in situ analysis of quench induced precipitation in a wide range of cooling rates varying between 0.0003 and 3 K/s. In 7003pure, three main precipitation reactions were observed during cooling, a medium temperature reaction with a distinct double peak between 325 and 175 °C and a very low temperature reaction starting at about 100 °C. An additional high temperature reaction related to the precipitation of Mg2Si starting at 425 °C has been observed for 7003Fe,Si,Zr. In terms of hardness after natural as well as artificial aging, alloy 7003pure shows a very low quench sensitivity. Hardness values on the saturation level of about 120 HV1 are seen down to cooling rates of 0.003 K/s. The as-quenched hardness (5 min of natural aging) shows a maximum at a cooling rate of 0.003 K/s, while slower and faster cooling results in a lower hardness. In terms of hardness after aging, 0.003 K/s could be defined as the technological critical cooling rate, which is much higher for 7003Fe,Si,Zr (0.3–1 K/s). The physical critical cooling rates for the suppression of any precipitation during cooling were found to be about 10 K/s for both variants.

Effect of arc stud welding parameters on the microstructure and mechanical properties of AA6061 and AA5086 aluminium alloys

Purpose: This paper aims to investigate the effect of arc stud welding (ASW) process parameters on the microstructure and mechanical properties of AA6061-T6 and AA5086-H116 joint. Design/methodology/approach: ASW process was done with argon as a shielding gas. Optical microscope (OM), scanning electron microscope (SEM), and X-Ray Diffraction (XRD) were employed to investigate the influence of welding current, welding time, and gas flow-rate on the microstructure of the fusion zone (FZ). Torque strength and Microhardness tests were used to evaluate the mechanical properties of the welded joints. Findings: OM and SEM showed a cellular dendritic structure with equiaxed zone and columnar dendritic are forming at welding zone and weld interface. XRD analysis showed the precipitation of Mg2Si and Al3Mg2 in the similar and dissimilar joints. Similar ASW of AA6061-T6/AA6061-T6 recorded 19 N.m torque strength, while dissimilar welding of AA6061-T6/AA5086-H116 registered 23 N.m. With increasing heat input, grains in Fusion Zone (FZ) and Heat Affected Zone (HAZ) coarsen and the hardness in both zones decreased. The hardness of similar weldments indicated a remarkable softening of FZ, while lower hardness values were registered in HAZ of dissimilar weldments. Softening of both weldments is due to the dissolution of the strengthening precipitates. Hot cracks exist with similar weldments, while no cracks evidence with dissimilar weldments. Research limitations/implications: The main challenge in this work was how to minimize porosity level and how to avoid hot crack in the FZ. Practical implications: The application of ASW with ceramic ferrule has an important role in different production areas such as; automobile industry, aircraft applications, and appliances industry. Originality/value: Study the effect of welding current, welding time, and gas flow-rate of ASW process on microstructure and mechanical properties of AA6061-T6 and AA5086-H116 joint.

An additively manufactured and direct-aged AlSi3.5Mg2.5 alloy with superior strength and ductility: micromechanical mechanisms

An AlSi3.5Mg2.5 (wt%) alloy with excellent mechanical properties was produced via laser powder bed fusion in this study. The yield strength, tensile strength, and elongation of this as-built AlSi3.5Mg2.5 alloy reach about 406 MPa, 501 MPa, and 8.6%, respectively. These properties are dramatically superior to the current additively manufactured Al-Si-Mg alloys. A direct-aging treatment at 170°C for one hour increases the yield strength and ductility further to about 417 MPa and 11.0%, respectively, with the tensile strength remaining the same level. The microstructures and strengthening mechanisms of the as-built and direct-aged samples were investigated systematically. The underlying micromechanical mechanisms of the as-built and direct-aged samples were examined based on a combination of in-situ synchrotron X-ray diffraction and three-dimensional crystal plasticity modeling. The as-built AlSi3.5Mg2.5 alloy possesses a fine microstructure, including fine grains and nano-sized Mg2Si and Si precipitates. After direct-aging treatment, additional Mg2Si and Si precipitate out. Besides, element diffusion upon aging treatment causes migration of cell boundaries and relaxation of residual stress. The direct-aging treatment leads to an increased Orowan strengthening, dislocation strengthening, and load-bearing strengthening effects. Moreover, the variations of microstructure and residual stress after the aging treatment change the dislocation behavior and increase the dislocation storage capacity, causing an increased ductility. Nevertheless, the aging treatment does not alert the type of damage and fracture. This study provides valuable insights to tailor the microstructure and mechanical properties of additively manufactured Al-Si-Mg alloys.

Probability-Dependent Precipitation Strengthening Effect of Anisotropic Precipitate in Al-Mg-Si Alloy Produced by T6 Heat Treatment

This study proposed a constitutive equation to predict the change in yield strength according to the behavior of β″ metastable precipitates, which have a profound effect on strength among materials precipitated during the T6 heat treatment of Al-Mg-Si alloy. The β″ precipitate is a metastable phase before it becomes a β (Mg2Si) precipitate, and is distributed in the form of nano-scale rods in the aluminum alloy matrix. Existing precipitation strengthening models assume the shape of the precipitate to be spherical, and in that case the equation that depends on the Orowan mechanism with the average precipitate size and distribution should dominate. However, precipitates are formed in various shapes and sizes by anisotropic growth. In particular, rod-shaped precipitates are not suitable for the existing precipitation strengthening model. In this study, an Al-Mg-Si alloy was fabricated by gravity casting followed by T6 heat treatment. The new precipitation strengthening effect equation proposes that the β″ precipitate affects yield strength during plastic deformation of the Al-Mg-Si alloy. The proposed precipitation strengthening effect equation probabilistically considers the Critical Resolved Shear Stress (CRSS), which varies depending on the angle between the dislocation and the precipitate, when the dislocation passes through a rod-shaped precipitate.

Influences of Heat Treatment on the Thermal Diffusivity and Corrosion Characterization of Al-Mg-Si alloy

The effect of the heat treatment on the Mg2Si phase in Al-Mg-Si alloy was investigated by a laser flash apparatus (LFA), Differential scanning calorimetry (DSC) and corrosion test. The alloy samples were solution treated at 590 oC for a half hour followed by warm water quenching, and then aged in air at 180, 200 and 240 oC for 5 hours. The results showed that the corrosion resistance of the solid solution treated sample was more improved than the as cast sample. Aging treatment also helped increase corrosion resistance at room temperature. It is thought that the fine Mg2Si precipitation phase on the grain had a more positive effect on improving corrosion resistance than crystallization of the Mg2Si phase on the grain boundaries. Corrosion rate also decreased with increasing aging treatment. The corrosion rate of AT240 was reduced to 1.16 MPY compared with the AT180 test piece, which had a corrosion rate of 3.79 MRY. The solution treated sample also showed lower thermal diffusivity than the aged samples. The thermal diffusivity increased as the solute concentration of Mg and Si in the a-Al matrix rapidly decreased during aging treatment. On the other hand, the thermal diffusivity of the aged samples, in which precipitation was completed by the aging process, decreased as the temperature rose. The thermal conductivities of all samples were similar near 250 oC when the β'' phase and β' precipitation was completed.

Study on microstructure characterization, electrical conductivity and mechanical property improvement mechanisms of a novel Al-Si-Mg-Fe-Cu alloy

A novel Al-4Si-0.8Mg-0.2Fe-0.1Cu with high strength, plasticity and electrical conductivity (EC) was developed successfully. The effects of Mg, Fe and Cu on microstructure, mechanical property and EC were systematically investigated. Interestingly, nano precipitates (nano AlFeSi and Mg2Si) not only acted as obstacles and sources of dislocation playing a precipitation strengthening role, but also the precipitation of AlFeSi and Mg2Si purified Al matrix to guarantee high EC. Thus EC and mechanical property of Al-4Si-0.8Mg-0.2Fe-0.1Cu alloy can be improved simultaneously. Results showed that EC of the alloy can reach 59.1%IACS (%IACS is short for International Annealed Copper Standard), the brinell hardness was 121 HBW, the ultimate tensile strength at room temperature (UTSRT) can reach 345 MPa and the corresponding elongation was 13%. The EC of Al-4Si-0.8Mg-0.2Fe-0.1Cu alloy was close to pure Al, and its corresponding mechanical properties were much higher than pure Al. So a kind of aluminum alloy conductive material with good EC and high strength was fabricated which has a certain application prospect in the field of overhead transmission line.