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.     

Microstructure and mechanical properties of Mg–Zn–(Nd)–Zr alloys with different extrusion processes

The effect of Nd addition and the in?uence of extrusion processes on the microstructure and mechanical properties of Mg–6Zn–0.5Zr(ZK60) and Mg–6Zn–1.5Nd–0.5Zr(ZKNd602) alloys were investigated. Nd element can obviously re?ne the microstructure of both as-cast and asextruded Mg–Zn–Nd–Zr alloy. All of the extruded alloys exhibit a bimodal grain structure composed of equiaxed?ne recrystallized(DRXed) grains and elongated coarse un DRXed grains. It is necessary to achieve high strength,particularly the yield strength, for ZKNd602 alloy, when it is extruded with a lower extrusion temperature, a suitable extrusion ratio and a relatively lower extrusion ram speed. In this study, the ultimate tensile strength(UTS),yield strength(YS) and elongation(El) of the extruded ZKNd602 alloy were 421 MPa, 402 MPa and 6.7 %,respectively, with extrusion temperature of 290 °C, extrusion ratio of 18:1 and a ram speed of approximate0.4 mm·s~(-1). Meanwhile, the extrusion process has obvious effects on the room-temperature properties but weak effects on the high-temperature properties.     

Microstructure,mechanical properties,and corrosion resistance of Mg–9Li–3Al–1.6Y alloy

Mg–9Li–3Al–1.6Y alloys were prepared through mixture method. The microstructure, mechanical properties, and corrosion resistance of the as-cast and asextruded alloys were studied by optical microscopy(OM),scanning electronic microscopy(SEM), X-ray diffraction(XRD), mechanical properties testing, and electrochemical measurement. The as-cast Mg–9Li–3Al–1.6Y alloy with the average grain size of 325 lm is composed of b-Li matrix, block a-Mg, and granule Al_2Y phases. After extrusion, the grain size of the as-cast alloy is obviously refined and reaches to 75 lm; the strength and elongation of the extruded alloy are enhanced by 17.20 % and49.45 %, respectively, owing to their fine microstructure and reduction of casting defects. The as-extruded alloy shows better corrosion resistance compared to the as-cast one, which may be related to the low stored energy and dislocation density in the extruded alloy, also the homogenization treatment before extrusion.     

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。     

Effects of extrusion and heat treatments on microstructure and mechanical properties of Mg–8Zn–1Al–0.5Cu–0.5Mn alloy

The effects of extrusion and heat treatments on the microstructure and mechanical properties of Mg–8Zn–1Al–0.5Cu– 0.5Mn magnesium alloy were investigated. Bimodal microstructure is formed in this alloy when it is extruded at 230 and 260 °C, and complete DRX occurs at the extruding temperature of 290 °C. The basal texture of as-extruded alloys is reduced gradually with increasing extrusion temperature due to the larger volume fraction of recrystallized structure at higher temperatures. For the alloy extruded at 290 °C, four different heat treatments routes were investigated. After solution + aging treatments, the grains sizes become larger. Finer and far more densely dispersed precipitates are found in the alloy with solution + double-aging treatments compared with alloy with solution + single-aging treatment. Tensile properties are enhanced remarkably by solution + double-aging treatment with the yield strength, tensile strength and elongation being 298 MPa, 348 MPa and 18%, respectively. This is attributed to the combined effects of fine dynamically recrystallized grains and the uniformly distributed finer precipitates.     

Effect of hot extrusion process on microstructure and mechanical properties of hypereutectic Al-Si alloys

The hypereutectic Al-Si alloy was fabricated by hot extrusion process after solidified under electromagnetic stirring,and the microstructure and mechanical properties of the alloy were studied.The results show that the ultimate tensile strength and elongation of the alloy reached 229.5 MPa and 4.6%,respectively with the extrusion ratio of 10,and 263.2 MPa and 5.4%,respectively with extrusion ratio of 20.This indicates that the mechanical properties of the alloy are obviously improved with the increase of extrusion ratio.After hot extruded,the primary Si,eutectic Si,Mg2Si,AlNi,Al7Cu4Ni and Al-Si-Mn-Fe-Cr-Mo phases are refined to different extent,and the efficiency of refinement is obvious more and more with the increase of extrusion ratio.After T6 heat treatment,the sharp corners of these phases become passivated and roundish,and the mechanical properties are improved.The ultimate tensile strength of the extruded alloy after T6 heat treatment reaches 335.3 MPa with extrusion ratio of 10 and 353.6 MPa with extrusion ratio of 20.     

Cold Spray Forming of Inconel 718

Inconel 718 was cold spray formed to a 6-mm thickness on an 8-cm diameter aluminum alloy tube using Sulzer Amdry 1718 powder and the Plasma Giken PCS-1000 cold spray system. The effects of spray particle velocity and post-spray heat treatment were studied. Post-spray annealing was performed from 950 to 1250 °C for 1-2 h. The resulting microstructures as well as the corresponding mechanical properties were characterized. As-sprayed coatings exhibited very low ductility. The tensile strength and ductility of the heat-treated coatings were improved to varying levels depending on the heat-treatment and spray conditions. For coatings sprayed at higher particle velocity and heat treated at 1250 °C for 1 h, an elongation of 24% was obtained. SEM micrographs showed a higher fraction of interparticle metallurgical bonds due to some sintering effect. Corresponding fracture surfaces also revealed a higher fraction of dimple features, typically associated with ductile fracture, in the annealed coatings. The results demonstrate that cold spray forming of Inconel 718 is feasible, and with appropriate heat treatment, metallurgical bonding can be increased. The ductility of the spray-formed samples was comparable to that of the bulk material.     

Swaging and heat treatment studies on sintered 90W–6Ni–2Fe–2Co tungsten heavy alloy

The effect of swaging deformation and low temperature aging on mechanical properties of tungsten heavy alloy (90W–6Ni–2Fe–2Co) was studied. The alloy was prepared by conventional hydrogen sintering followed by vacuum heat treatment and swaging with varying reductions in area (ranging from 10 to 75%). The swaged samples were aged in nitrogen atmosphere at temperatures ranging from 300 to 1100 °C followed by microstructure and mechanical property evaluation. Both microstructure and mechanical properties were sensitively dependent on the amount of deformation imparted during swaging. Subsequently, aging also influenced the properties depending upon the aging temperature. Detailed fractographic study revealed that the fracture mode of the alloy changed from intergranular to transgranular mode depending upon thermo-mechanical processing. Aging treatment after swaging affected the fracture morphology of alloy considerably. Samples aged at 500 °C showed predominant transgranular failure of tungsten grains, whereas the one heat treated at 700 °C showed increasing evidence ductile tear. Based on the results, an approach for optimizing mechanical properties that involves heat treatment and swaging operation was proposed.     

初始组织对热挤压Mg-6Al-2Ca-2Sm合金显微组织和力学性能的影响

对铸态Mg-6Al-2Ca-2Sm合金分别进行经固溶和固溶+时效处理获得不同初始组织试样,然后对不同初始组织的试样进行热挤压,研究了不同初始组织对热挤压Mg-6Al-2Ca-2Sm合金显微组织和力学性能的影响。结果表明：铸态合金经热挤压后发生明显的部分再结晶,显微组织得到显著细化;经固溶或固溶+时效处理能够改善合金组织,热挤压后合金显微组织分布更加均匀。初始组织分布能够改善热挤压Mg-6Al-2Ca-2Sm合金室温和高温力学性能,固溶+时效后进行热挤压,Mg-6Al-2Ca-2Sm合金具有最高的抗拉强度和延伸率。     

Preparation and properties of W–Cu–Zn alloy with low W–W contiguity

The W–Cu–Zn alloy with a-brass matrix and low W–W contiguity was prepared by method of electroless copper plating combined with spark plasma sintering(SPS) method.The effects of process and parameters on the microstructure and mechanical properties of the alloy were investigated.The W–Cu–Zn alloy with a relative density of 96 % and a W–W contiguity of about 10 % was prepared by original fine tungsten particles combined with wet mixing method and SPS solid-state sintering method at 800 °C for 10 min.The microstructure analysis shows that Cu–Zn matrix consists of nano-sized a-brass grains,and the main composition is Cu_3Zn electride.The nano-sized Cu was coated on the surface of tungsten particles by electroless copper plating method,and the fairly low consolidation temperature and short solid-state sintering time result in the nano-sized matrix phase.The dynamic compressive strength of the W–Cu–Zn alloy achieves to1000 MPa,but the alloy shows poor ductility due to the formation of the hard and brittle Cu_3Zn electrides.The fine-grain strengthening and the solution strengthening of the Cu–Zn matrix phase are responsible for the high Vickers microhardness of about 300 MPa for W–Cu–Zn alloy.     

Effect of heat treatment on microstructures and mechanical properties of A356 alloy cast through rapid slurry formation (RSF) process

The effect of T5 heat treatment on microstructure and mechanical properties of A356 alloy was observed. The as-cast A356 alloy exhibited coarse dendrites and long Si needles. RSF process changed the dendritic α-Al phase to globular morphology which helps in improving the mechanical properties of the alloy. The addition of 0.6wt-% Al–5Ti–1B grain refiner refined the average grain size of primary α-Al phase. T5 heat treatment at 170 °C for 20 h in different processing conditions was given to A356 alloy. T5 heat treatment led to further refinement of α-Al phase and Si needles, precipitation hardening due to Mg₂Si phase and reduction in the porosity level (%). The Quality Index for A356 alloy in different processing conditions was also measured. Results showed that RSF process with the use of baffles, addition of grain refiner and T5 heat treatment had improved the mechanical properties over other processing conditions.     

Microstructure,Phase Transformations,and Properties of Hot-Extruded Ni-Rich NiTi Shape Memory Alloy

Processing of NiTi shape memory alloys strongly influences their microstructure, phase transformations, mechanical, and shape memory properties. Hot forging, hot swaging, or hot rolling are efficient techniques for obtaining the desired shape, but during multiple operations the material must be heated and worked in the temperature range from 700 to 900 °C. During these processes, intense oxidation takes place. In order to reduce it, the hot-pack working is applied. The hot extrusion is more effective for reduction of ingot, billet, and rod diameters than hot forging, hot swaging, or hot rolling. Also, during hot extrusion the material surface undergoes considerably less oxidation. In the present work, results of the characterization by differential scanning calorimetry, low-temperature x-ray powder diffraction, and three-point bending and free recovery ASTM F2082-06 tests of the samples after hot direct extrusion and heat treatment are presented. The obtained alloy after hot direct extrusion exhibits desired shape memory effect. The phase transformations during cooling and heating cycle occur with the presence of the R phase. The range of the characteristic temperatures for the obtained material gives possibility for further medical applications. After annealing at 400 and 500 °C, the characteristic temperatures shift to higher values.     

Enhancing room temperature mechanical properties of Mg–9Al–Zn alloy by multi-pass equal channel angular extrusion

Influence of equal channel angular extrusion on room temperature mechanical properties of cast Mg–9Al–Zn alloy was investigated. The results show that room temperature mechanical properties of Mg–9Al–Zn alloy, such as yield strength, ultimate tensile strength and elongation, can be improved heavily by equal channel angular extrusion. Processing routes, processing temperature and extrusion passes have important influence on room temperature mechanical properties of processed Mg–9Al–Zn alloy by equal channel angular extrusion. The optimum room temperature mechanical properties such as yield strength of 209 MPa, ultimate tensile strength of 339 MPa and elongation of 14.1%, can be obtained when Mg–9Al–Zn alloy was processed by equal channel angular extrusion for 6 passes at route B_C at 498 K. Large bulk materials of Mg–9Al–Zn alloy with average grain size of 4 μm and high mechanical properties can be prepared.     

变形及热处理对Al-Sc二元合金力学性能与导电性能的影响

研究了Al-x Sc(x=0、0.10%、0.45%、0.70%)合金在挤压变形、拉拔变形和热处理过程中的力学性能和导电性能的变化。结果表明,铸态Al-Sc二元合金的强度都随Sc含量的增加而增加,而电导率逐渐降低。挤压变形后,Al-Sc合金的晶粒均有所细化,屈服和抗拉强度大幅提升,塑性略有下降;拉拔变形后,加工硬化使各Al-Sc合金的强度进一步提高,伸长率大幅降至1%左右;经过400℃保温2 min+300℃保温150 min的热处理后,Al-Sc合金的伸长率大幅提升,纯铝和Al-0.1%Sc合金的强度降低,然而添加0.45%和0.70%Sc的合金强度却有所升高,这主要是由于热处理后含Sc第二相析出导致的。两种变形过程对Al-Sc合金电导率的影响很小,热处理可通过分解铝钪固溶体大幅提高Al-Sc合金的电导率。最终制备的Al-0.45%Sc合金屈服强度,伸长率和电导率分别为210 MPa,7.2%,34.8×10^6S/m,兼具良好的力学性能和导电性能。     

Microstructure and mechanical properties of 7075 aluminum alloy during complex thixoextrusion

7075 aluminum alloy was used to obtain elbow parts by complex thixoextrusion and the microstructure evolution and mechanical properties during this process were studied by SEM, TEM and other analytical methods. The results show that different parts in 7075 aluminum alloy show quite different microstructures. The microstructure of the thin walls formed by back-extrusion is stratified, and the bottom of the parts formed by angular extrusion is obviously deformed. Shear forces contribute to the crushing of grains and the coarse second phase. The main strengthening phases in the material are η phase and E phase, whose amounts greatly decrease during heating to semi-solid and thixoextrusion. After heat treatment, they can precipitate evenly to improve the mechanical properties of the material. The average tensile strength of whole part after thixoextrusion and heat treatment is 485.49 MPa, while the average elongation is 5.49%.     

热挤压对7055铝合金力学性能及组织的影响

采用挤压铸造成形工艺制备7055高强铝合金,研究了热挤压参数对合金力学性能及微观组织的影响,并与铸态下的力学性能及微观组织进行了对比.结果表明,热挤压态下的7055铝合金的微观组织和力学性能均优于铸态,并且晶粒随着比压的增加趋于细化,抗拉强度随着比压的增加趋于提高.当比压为75 MPa时,在730 ℃温度下进行挤压浇注,经过双级固溶处理和时效后,合金的晶粒明显细化,抗拉强度达到681.4 MPa,伸长率达到7.14%.     

Influence of short-term heat treatment on the microstructure and mechanical properties of EN AW-6060 T4 extrusion profiles: Part A

Aluminium alloys are applied in various industrial fields and play an important role concerning weight reduction especially in the automotive industry. Because of their higher strength, age-hardening alloys are commonly preferred. However, the cold formability in comparison to other materials like mild steels is quite low and due to this, complex parts are hardly producible at higher temperatures. One possibility to improve the cold formability of aluminium alloys is the so called tailor heat treatment. In this approach, a short-term heat treatment is conducted to achieve a local softening of the material due to dissolution of strengthening clusters (retrogression). This effect is used to improve the material flow, relief critical forming zones and enhance the overall formability of the material. Afterwards, strength can be increased again by aging. However, up till now tailor heat treatment has mainly been used for aluminium sheet. Further, a holistic process understanding, taking into account all process parameters as well as a complete integration of microstructural findings is missing. Therefore, the dissolution and precipitation behaviour during heating of Tailor Heat Treated Profiles (THTP) from the aluminium alloy EN AW-6060 T4 is investigated. Heating curves from 20 to 600 °C with heating rates of 0.01 up to 5 K/s are recorded, using the differential scanning calorimetry (DSC). Based on the peak temperatures of one DSC-curve, tensile tests were carried out after a comparable heat treatment. It is shown, that the mechanical properties gained by the tensile test correlate with the microstructure results of the DSC measurements. The correlation of the microstructure and the mechanical properties enables the derivation of optimal parameters for the development of THTP through a local softening. In Part B the heat treatment parameter for the subsequent forming process as well as the evolution of the mechanical properties during natural aging after different short-term heat treatments are discussed.     

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.     

Effects of Sintering and Extrusion on the Microstructures and Mechanical Properties of a SiC/Al-Cu Composite

This article studied the effects of sintering and extrusion on the microstructures and mechanical properties of SiC particle reinforced Al-Cu alloy composite produced by powder metallurgy method. It has been shown that both extrusion and increasing sintering temperature can significantly improve the strength and plasticity of the composite. The extrusion and increase of the sintering temperature can break up the oxide coating on the matrix powder surfaces, decrease the number of pores, accelerate the elements’ diffusion and increase the density and particle interfacial bonding strength, thus significantly improve the mechanical properties of the composite. The strength and hardness of the composite increase and the elongation decreases with increasing the aging time at under-aged stage, while the strength and hardness start to decrease and the elongation starts to increase with increasing the aging time at over-aged stage due to the formation and growth of the secondary strengthening precipitates in the Al-Cu matrix.     

Microstructure and Mechanical Properties of a Mg94Y4Ni2 Alloy with Long Period Stacking Ordered Structure

Microstructure and mechanical properties of the Mg₉₄Y₄Ni₂ alloy (at.%) during homogenization, extrusion, and aging processes were systematically investigated using x-ray diffractometer, optical microscopy, scanning electron microscopy, transmission electron microscopy, and electronic universal testing machine. The results showed that the morphology evolution of 18R LPSO structure during annealing in Mg₉₄Y₄Ni₂ alloy was different from that of Mg-Y-Zn systems. The 18R-type Mg₁₂YNi phase was thermal stable and was not transformed into 14H structure when annealed at 773 K. After solution treatment at 773 K for 10 h and aging at 498 K for 24 h (T6 treatment) of the extruded alloy, a great amount of fine β′ phases were precipitated dispersedly in the matrix. The tensile tests showed that the extruded Mg₉₄Y₄Ni₂ alloy after T6 treatment exhibited good tensile properties with ultimate tensile strength of 453 MPa and elongation to failure of 2.4% at room temperature. Thus, a high-strength Mg₉₄Y₄Ni₂ alloy, which is strengthened by the coexisted LPSO phases and β′ precipitates, can be prepared via simple hot extrusion and T6 treatment.