Effect of heat treatment on microstructure and properties of semi-solid squeeze casting AZ91D

Semi-solid AZ91D magnesium alloy billets were prepared by near-liquidus heat holding. Semi-solid squeeze casting was conducted at 575, 585 and 595 ℃, respectively, with 1 mm·s~(-1) squeeze speed. The semisolid squeeze casting AZ91D samples were heat treated by T4(solution at 415 ℃ for 24 h) and T6(solution at 415 ℃ for 24 h + 220 ℃ for 8 h) processes, respectively. The microstructure and mechanical properties of the alloy in different states were investigated by means of OM, SEM and tensile testing machine. The results show that compared to as-cast alloy, the grain size of the semi-solid squeezed AZ91D decreased significantly, and with the increase of semi-solid squeeze temperature, the grain size of AZ91D increased. The grains of the alloy were refined by T4 treatment, and further refined by T6 treatment. T6 treatment greatly improved the tensile strength, elongation, and hardness, but did not significantly improve yield strength. After 575 ℃ squeeze casting and T6 treatment, the ultimate tensile strength(UTS) reached 285 MPa, the elongation reached 13.36%, and the hardness also reached the maximum(106.8 HV), but the yield strength(YS) was only 180 MPa. During the process of semi-solid squeeze casting and heat treatment, the matrix grain was refined and a large number of precipitated and secondary precipitated phases of Mg_(17)Al_(12) appeared. Both the average size of matrix grain and secondary precipitated phase decreased, while the volume fraction of secondary precipitated phase increased. All these resulted in high tensile strength, elongation and hardness.     

Effect of thermal exposure on the microstructure,tensile properties and the corrosion behaviour of 6061 aluminium alloy sheet

Sheet material of the Al‐Mg‐Si alloy 6061 in the tempers T4 and T6 was thermally exposed at temperatures ranging from 85 to 120°C for 1000 h. The microstructure, tensile properties and the corrosion behaviour in the different heat treatment conditions were investigated using differential scanning calorimetry and transmission electron microscopy as well as performing tensile tests and various corrosion tests. The additional heat treatments, which should simulate aging during long‐term service usage, caused an increase in strength of 6061‐T4 sheet, associated with changes in the naturally aged microstructure. Thermal exposure at 120°C for 1000 h resulted in tensile and corrosion properties being similar to those obtained for peak‐aged sheet. Alloy 6061 in the T6 temper exhibited microstructural stability when additionally heat treated at 85 and 120°C for 1000 h. No significant alterations in the microstructure, tensile properties, and corrosion performance were observed after exposure to slightly elevated temperatures.     

Optimization of heat treatment of gravity cast Sr-modified B356 aluminum alloy

In recent years, certain foundry processes have made it possible to obtain products with very thin parts, below the 4 mm threshold of the permanent mold casting technology. The safety margins of these castings have been reduced, so the T6 heat treatment conditions adopted for the Al–7Si–Mg alloys need to be investigated to identify the best combination of strength and ductility. Furthermore, the cost and the production time associated with T6 heat treatment have to be optimized. In the present work, an experimental study was carried out to optimize the solution treatment and artificial aging conditions in gravity cast thin bars of B356 aluminum alloy modified with Sr. Two solution temperatures were selected, 530 °C and 550 °C, respectively, with solution time ranging from 2 to 8 h, followed by water quenching and artificial aging at 165 °C with aging time from 2 to 32 h. The results of hardness and tensile tests were correlated with differential scanning calorimetry (DSC) analysis. The best combination of mechanical properties and heat treatment duration was obtained with 2 h solutionizing at 550 °C and 8 h aging at 165 °C. DSC analysis showed that the alloy's mechanical properties reach the maximum value when the β″ phase is completely developed during the artificial aging.     

Effect of heat treatment on tensile and fatigue deformation behavior of extruded Al-12 wt%Si alloy

This study investigated the effect of heat treatment on tensile and high-cycle fatigue deformation behavior of extruded Al-12 wt%Si alloy. The material used in this study was extruded at a ratio of 17.7: 1 through extrusion process. To identify the effects of heat treatment, T6 heat treatment (515 °C/1 h, water quenching, and then 175 °C/10 h) was performed. Microstructural observation identified Si phases aligned in the extrusion direction in both extruded alloy (F) and heat treated alloy (T6). The average grain size of F alloy was 8.15 °C, and that of T6 alloy was 8.22 °C. Both alloys were composed of Al matrix, Si, Al₂Cu, Al₃Ni and AlFeSi phases. As T6 heat treatment was applied, Al₂Cu phases became more finely and evenly distributed. Tensile results confirmed that yield strength increased from 119.0 MPa to 329.0 MPa, ultimate tensile strength increased from 226.8 MPa to 391.4 MPa, and the elongation decreased from 16.1% to 5.0% as T6 heat treatment was applied. High-cycle fatigue results represented F alloy’s fatigue limit as 185 MPa and T6 alloy’s fatigue limit as 275 MPa, indicating that high-cycle fatigue properties increased significantly as heat treatment was conducted. Through tensile and fatigue fracture surface analysis, this study considered the deformation behaviors of extruded and heat treated Al-Si alloys in relation to their microstructures.     

固溶处理和人工时效对Al-Cu合金显微组织和力学性能的影响(英文)

对Al-Cu合金进行析出强化和人工时效处理以获得优异的力学性能,如高的强度、好的韧性。其热处理工艺条件为:510～530℃固溶处理2h;60℃水淬;160～190℃人工时效2～8h。采用光学显微镜、扫描电镜、能谱分析、透射电镜和拉伸实验对经固溶和人工时效处理的Al-Cu合金的组织和力学性能进行表征。固溶处理实验结果表明,Al-Cu合金的力学性能随着固溶处理温度的升高先增加,然后降低。这是由于Al-Cu合金的残余相逐渐溶解进入基体中,从而导致析出相的数量和再结晶晶粒尺寸不断增加。相较于固溶处理温度,固溶处理时间对Al-Cu合金的影响较小。人工时效处理实验结果表明,合金经180℃时效8h,可以获得最大的拉伸强度。合金的最大拉伸强度和屈服强度随着时效时间的延长和温度的升高而升高。     

Low Solution Temperature Heat Treatment of AlSi<Subscript>9</Subscript>Cu<Subscript>3</Subscript>(Fe) High-Pressure Die-Casting Actual Automotive Components

Usually, high-pressure die-casting (HPDC) components cannot be heat-treated at high temperature without the occurrence of surface blisters, which are unacceptable for surface finish and may reduce the mechanical properties. In this context, the purpose of the present paper was to analyze the effectiveness of special low solution temperature T6 heat treatment in overcoming this limit for HPDC AlSi₉Cu₃ alloy. Very low solution temperatures (<?450 °C, followed by 165 °C aging) to prevent the occurrence of blisters were combined with commonly used times (from 1 to 16 h) ensuring the feasibility of industrial application. Treatments were conducted on samples extracted from actual castings to evaluate the typical defects encountered in common production. Properties were analyzed by means of visual inspection, microstructural observations, image analysis, hardness, tensile tests and fractography. The results showed that it is possible to use solubilization temperatures below 450 °C for several hours in a T6 treatment to give strengthening without relevant blistering in AlSi₉Cu₃ alloy. The optimum match of properties was provided by a solution treatment at 430 °C for 4 h followed by an aging at 165 °C for 8 h, which gave a yield increase of ~?50 MPa, an increase in ductility and the best Quality Index value.     

Retrogression and re-aging treatment of Al-9.99%Zn-1.72%Cu-2.5%Mg-0.13%Zr aluminum alloy

1 Introduction The 7000 series aluminum alloys have been widely used as aircraft structure material because of their high strength/density ratio. This series of alloys provide high strength in the T6 condition but are prone to stress corrosion cracking(SC…     

Effect of multi-temperature aging on the characterization of aluminum based castings heat treated using fluidized bed technique

The current study investigates the influences of the fluidized bed heat treatment on the quality indices and microstructural characterization of A356.2 and B319.2 castings. Traditional heat treatment technology, employing circulating air convection furnaces (CF), was used to establish a relevant comparison with fluidized sand bed (FB) for the heat treatment of the alloys investigated, employing T6 continuous aging cycles or multi-temperature aging cycles. The results of alloys subjected to multi-temperature aging cycles reveal that the strength results obtained after the T6 continuous aging treatment of A356 alloys are not improved by means of multi-temperature aging cycles, indicating therefore that the optimum properties are obtained using a T6 aging treatment. The optimum strength properties of B319.2 alloys, however, is obtained by applying multi-temperature aging cycles such as, for example, 230 °C/2 h followed by 180 °C/8 h, rather than T6 aging treatment. In the case of multi-temperature aging cycles, the modification factor has the most significant role in improving the quality index values of 356 and 319 alloys. The FB heattreated alloys have the highest strength values for all heat treatment cycles compared to CF heat-treated alloys; however, the FB has no significant effect on the quality values of 319 alloys compared to the CF.     

Tribological Behavior of a Heat-Treated Cobalt-Based Alloy

The present study reviews the tribological behavior of a Co-Cr-Mo alloy regarding to microstructural changes caused by solution and aged heat treatments. The influence of microstructure on wear resistance was assessed in a pin-on-disk configuration. It was found that after a long solution heat treatment of 6 h at 1200 °C, most of the carbides were dissolved into the matrix, and coarse grain size was obtained. Solution treatment for 1 h presented fine grains and globular carbides along the matrix. Aging at 850 °C resulted in a quantity of phase transformation which was different from austenite face cubic centered to martensite hexagonal close packed (HCP); 35% of HCP was reached during 8 h of treatment and 60% for 15 h. As-cast condition and 6-h solution heat treatment exhibited the greatest wear loss, while 1-h solution treatment and samples containing HCP phase showed a threefold lower wear.     

Effects of solution heat treatment on the microstructure, oxidation, and mechanical properties of a cast Ni3Al-based intermetallic alloy

Solution heat treatment is employed in an attempt to improve oxidation and mechanical properties of an as-cast Ni₃Al alloy (IC221M) at operation temperature, 900 °C. Solution heat treatment was hypothesized to have beneficial effects through dissolving γ Ni₅Zr eutectic into the matrix. The microstructures, oxidation behavior in air at 900 °C, and mechanical properties with aging times at 900 °C were examined after solution heat treatment of as-cast Ni₃Al alloy in Ar for up to 100 h at 1100 °C. The oxide penetration depth into the matrix was dramatically decreased and more homogeneous surface oxides were obtained relative to the no solution, treatment case. Hardness was improved by solution heat treatment due to a solid solution strengthening effect by Zr, but the tensile properties after solution heat treatment were not significantly different from those prior to treatment.     

Effects of heat treatment on phase contents and mechanical properties of infiltrated B4C/2024Al composites

The B₄C/2024Al composites were successfully produced by pressureless infiltration method, and the effects of heat treatment on phase content and mechanical properties were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and mechanical properties testing. The results show that phases of B₄C/2024Al composites include B₄C, Al, Al₃BC, AlB₂ and Al₂Cu. The phase species remain unchanged; however, the phase content of the composites changes significantly after heat treatment at the temperature of 660, 700, 800 or 900 °C for 12, 24 or 36 h. It is found that the heat treatment results in not only considerable enhancement in hardness, but also reduction in bending strength of the composites. Heat treatment at 800 °C for 36 h does best to hardness of the composites, while at 700 °C for 36 h it is the most beneficial to their comprehensive mechanical properties.     

Microstructure Evolution and Mechanical Properties of 2219 Al Alloy During Aging Treatment

Hardness and tensile properties of 2219 Al alloys were tested at various temperature (150, 165, 175 °C) and subjected to T6 temper heat treatment to identify the peak aging time at various temperature. Microstructure evolution and precipitate behavior were analyzed with transmission electron microscope (TEM), differential scanning calorimetry (DSC) and x-ray diffraction (XRD). It is found that the peak aging time is 24 h at 150 °C and does not vary down to 165 °C. When the aging temperature rise to 175 °C, the peak aging time down to 12 h. Considering the strength and elongation, the optimum aging treatment is at 165 °C for 24 h after the solution treatment at 535 °C for 1.5 h. Compared with that of only water-quenched sample, after aged at 165 °C for 24 h, the tensile strength of the 2219 Al alloy increases from 324.5 to 411.8 MPa, yield strength from 168 to 310.8 MPa, respectively. The improvement in the mechanical performance is mainly attributed to the precipitation strengthening of the GP zones, θ″ and θ’ phases.     

The Effect of the Surface Treating and High-Temperature Aging on the Strength and SCC Susceptibility of 7075 Aluminum Alloy

A novel heat-treatment procedure combining the shot-peening with a two-step aging operation was proposed to improve both the strength and the stress corrosion cracking (SCC) resistance of the high-strength 7075 aluminium alloy. The heat treatment included one shot-peening stage before or between the two stages of aging at 120 °C for 24 h and at 160 °C for 1 h, respectively. The mechanical properties obtained during the aforementioned operations were extremely similar to those of the T6 sample owing to the unaffected bulk microstructure over such a low over-aging period. The SCC resistance of these samples was considerably improved compared to that of the T6 sample and of the conventional shot-peened T6 sample due to the over-aging of the surface like the T7 treatment leading from the diffusion acceleration by the dislocations generated in the surface layer during shot-peening. In spite of the further depth of deformation caused by shot-peening prior to the first step of aging, the sample shot-peened after the first step of aging showed no significant decrease in the SCC resistance because of its higher generated dislocation by shot-peening.     

流变轧制AZ91合金的热处理和组织性能调控

本文对连续流变轧制AZ91合金在热处理过程中的组织和力学性能演化进行了研究。热处理后两种析出相在基体中出现：一种是晶界处的非连续析出相,另一种是从过饱和基体中析出的小尺寸连续析出相。随着时效温度升高,原子扩散速度也随之提高,导致更多的析出相生成和长大。合金的维氏硬度和拉伸强度峰值在16小时时效后出现,而合金的延伸率随着时效时间的延长和时效温度的提高呈下降趋势。经过对实验结果的分析,适合提升合金综合力学性能的热处理制度为415°C固溶20小时加220°C时效16小时。经热处理后得到的维氏硬度、拉伸强度和延伸率分别为：99 HV,251 MPa和4.5%,各项性能均显著优于流变轧制态合金。相对于传统成型手段,流变轧制加热处理方法成型的AZ91合金展现了优异且均衡的综合力学性能。     

Heat Treatment Development for a Rapidly Solidified Heat Resistant Cast Al-Si Alloy

Existing heat treatment standards do not properly define tempers for thin-walled castings that solidified with high solidification rates. Recently emerged casting processes such as vacuum high pressure die casting should not require long solution treatment times due to the fine microstructures arising from rapid solidification rates. The heat treatment studies involving rapidly solidified samples with secondary dendrite arm spacing between 10 and 35 μm were conducted for solution times between 30 min and 9 h and temperatures of 510 and 525 °C and for various aging parameters. The metallurgical analysis revealed that an increase in microstructure refinement could enable a reduction of solution time up to 88%. Solution treatment resulted in the dissolution of Al₂Cu and Al₅Mg₈Si₆Cu₂, while Fe- and TiZrV-based phases remained partially in the microstructure. The highest strength of approximately 351 ± 9.7 and 309 ± 3.4 MPa for the UTS and YS, respectively, was achieved for a 2-step solution treatment at 510 and 525 °C in the T6 peak aging conditions, i.e., 150 °C for 100 h. The T6 temper did not yield dimensionally stable microstructure since exceeding 250 °C during in-service operation could result in phase transformation corresponding to the over-aging reaction. The microstructure refinement had a statistically stronger effect on the alloy strength than the increase in solutionizing time. Additionally, thermal analysis and dilatometer results were presented to assess the dissolution of phases during solution treatment, aging kinetics as well as dimensional stability.     

Influence of solution heat treatment on microstructure and stress rupture properties of a Ni3Al base single crystal superalloy IC6SX

The effect of solution heat treatment at different temperatures on the microstructure and stress rupture properties of a Ni₃Al base single crystal superalloy IC6SX has been investigated in this paper. The experimental results show that the as-cast alloy exhibited a typical dendritic structure with three phases of γ′, γ and NiMo. After solution heat treated at 1240 °C, the NiMo phase dissolved entirely. With the temperature increasing, the γ′ phase in interdendritic region dissolved earlier than that in dendritic region. When solution heat treatment temperature reached to 1280 °C, all of the γ′ solutioned and a uniform microstructure was observed. Furthermore, increasing the temperature up to 1340 °C, a small amount of incipient melting occurred in the alloy. The stress rupture life of IC6SX at 1100 °C/130 MPa increased with the rising of temperature and reached to the top value under the solution heat treatment temperature of 1280 °C. The optimum solution heat treatment considered to be 1280 °C/10 h followed by flowing air cooling.     

Synergistic effects of composition and heat treatment on microstructure and properties of vacuum die cast Al-Si-Mg-Mn alloys

The purpose of this study was to prepare high-quality Al-Si-Mg-Mn alloy with a good combination of strength and ductility employing the vacuum-assisted high-pressure die cast process. An orthogonal study of heat treatments was conducted to design an optimized T6 heat treatment process for both Al-10%Si-0.3%Mg-Mn and Al-11%Si-0.6%Mg-Mn alloys. The results demonstrate that no obvious blisters and warpage were observed in these two alloys with solid solution treatment. After the optimal T6 heat treatment of 530°C×3 h + 165°C×6 h, Al-11%Si-0.6%Mg-Mn alloy has better mechanical properties, of which tensile strength, yield strength and elongation reached 377.3 MPa, 307.8 MPa and 9%, respectively. The improvement of mechanical properties can be attributed to the high density of needle-like β″(Mg_5Si_6) precipitation after aging treatment and the fine and spherical eutectic Si particles uniformly distributed in the α-Al matrix.     

Effect of secondary aging on microstructure and properties of cast Al-Cu-Mg alloy

To obtain better comprehensive properties of cast Al-Cu-Mg alloys, the secondary aging (T6I6) process (including initial aging, interrupted aging and re-aging stages) was optimized by an orthogonal method. The microstructures of the optimized Al-Cu-Mg alloy were observed by means of scanning electron microscopy and transmission electron microscopy, and the properties were investigated by hardness measurements, tensile tests, exfoliation corrosion tests, and intergranular corrosion tests. Results show that the S phase and θ′ phase simultaneously exist in the T6I6 treated alloy. Appropriately increasing the temperature of the interrupted aging in the T6I6 process can improve the mechanical properties and corrosion resistance of Al-Cu-Mg alloy. The optimal comprehensive properties (tensile strength of 443.6 MPa, hardness of 161.6 HV) of the alloy are obtained by initial aging at 180 °C for 2 h, interrupted aging at 90 °C for 30 min, and re-aging at 170 °C for 4 h.

     

Effect of bonding temperature and heat treatment on microstructure and mechanical property of Mg−6Gd−3Y alloy vacuum diffusion bonded joints

Diffusion bonding of as-cast Mg?6Gd?3Y magnesium alloy was carried out at temperatures of 400?480 °C with bonding pressure of 6 MPa for 90 min. Diffusion bonded joints were solution treated at 495 °C for 14 h and then aged at 200 °C for 30 h. Microstructures and mechanical properties of joints were analyzed. The results showed that rare earth elements and their compounds gathering at bonding interface hindered the grain boundary migration crossing bonding interface. Tensile strength of as-bonded and as-solution treated joints increased firstly and then decreased with the bonding temperature increasing due to the combined effects of grain coarsening and solid-solution strengthening. As-bonded and solution-treated joints fractured at matrix except the joint bonded at 400 °C, while aged joints fractured at bonding interface. The highest ultimate tensile strength of 279 MPa with elongation of 2.8% was found in joint bonded at 440 °C with solution treatment followed by aging treatment.     

Effects of Heat Treatment on the Microstructures and High Temperature Mechanical Properties of Hypereutectic Al–14Si–Cu–Mg Alloy Manufactured by Liquid Phase Sintering Process

Hypereutectic Al–Si alloy is an aluminum alloy containing at least 12.6 wt.% Si. It is necessary to evenly control the primary Si particle size and distribution in hypereutectic Al–Si alloy. In order to achieve this, there have been attempts to manufacture hypereutectic Al–Si alloy through a liquid phase sintering. This study investigated the microstructures and high temperature mechanical properties of hypereutectic Al–14Si–Cu–Mg alloy manufactured by liquid phase sintering process and changes in them after T6 heat treatment. Microstructural observation identified large amounts of small primary Si particles evenly distributed in the matrix, and small amounts of various precipitation phases were found in grain interiors and grain boundaries. After T6 heat treatment, the primary Si particle size and shape did not change significantly, but the size and distribution of CuAl₂ (θ) and AlCuMgSi (Q) changed. Hardness tests measured 97.36 HV after sintering and 142.5 HV after heat treatment. Compression tests were performed from room temperature to 300 °C. The results represented that yield strength was greater after heat treatment (RT?~?300 °C: 351?~?93 MPa) than after sintering (RT?~?300 °C: 210?~?89 MPa). Fracture surface analysis identified cracks developing mostly along the interface between the primary Si particles and the matrix with some differences among temperature conditions. In addition, brittle fracture mode was found after T6 heat treatment.