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

The effects of Ag on the microstructure and mechanical properties of 2519 aluminum alloy were investigated by means of tensile test, micro-hardness test, transmission electron microscope and scanning electron microscope. The results show that the addition of 0.3 % （mass fraction） Ag accelerates 2519 aluminum alloy＇s age-hardening, increases its peak hardness and reduces 4 h of peak aged time at 180 ℃. The addition of 0. 3% （mass fraction） Ag increses the tensile strength at room temperature and elevated temperature. This increment at room temperature and 200 ℃ is 24 MPa and 78 MPa, respectively. In contrast, the elongation of 2519 aluminum alloy is decreased with Ag addition. The increase of tensile strength of 2519 aluminum alloy with Ag addition is attributed to the high volume fraction of Ω phase.     

Effects of cryogenic treatment on mechanical properties of extruded Mg-Gd-Y-Zr（Mn） alloys

The influence of cryogenic treatment on the mechanical properties of the extruded Mg-Gd-Y-Zr（Mn） alloys was investigated by the tensile tests, scanning electron microscopy（SEM）, transmission electron microscopy（TEM）, and energy dispersive X-ray spectroscopy （EDS）. The results show that the mechanical properties of both alloys are improved greatly during the in situ tensile test by soaking the samples in liquid nitrogen for 10 min. The ultimate tensile strength, yield tensile strength and elongation of cryogenic treated magnesium alloy added with zirconium or manganese are largely elevated. And remarkable microstructure change is observed in both alloys by cryogenic treatment. There are a large number of twins, rod-like, tree-like and chrysanthemum-like precipitated phases in the microstructures and the fracture surfaces exhibit the characteristics of ductile rupture when they are observed at room temperature.     

Microstructure and RRA treatment of LFEC 7075 aluminum alloy extruded bars

The microstructures after casting and extruding, the mechanical properties and electrical conductivity after RRA treatment of conventional DC casting and low frequency electromagnetic casting (LFEC) 7075 aluminum alloy were investigated. The results showed that finer grains which distributed more homogeneously was obtained in LFEC ingots compared with those conventional DC ingots. The extruded bars of LFEC alloy kept its fine grain features of original as-cast structure. In the RRA treatment, with the extension of second aging time, the tensile strength and hardness of alloy decreased, but the electrical conductivity increased. Meanwhile, as the second aging temperature raised, the phase change rate in precipitation also increased. Under the same conditions, extruded bars of LFEC alloy had better performance than that of conventional DC cast alloy. The optimum RRA heat treatment process was 120 ℃/24 h+180 ℃/30 min+120 ℃/24 h. The LFEC extruded bars acquired tensile strength 676.64 MPa, hardness 198.18, and electrical conductivity 35.7% IACS respectively, which were higher than that in the T6 temper, indicating that a notable RRA response takes place in LFEC extruded bars, whose second-step retrogression time was 30 min, and it was suitable for mass production.     

Mechanical properties and microstructure of TRIP steels produced using TSCR process

C-Si-Mn TRIP steels were produced using the thin slab casting and rolling （TSCR） process under simulation in laboratory. The results of tensile tests show that the yield strength, tensile strength, and the total elongation of the experimental TRIP steels are 430 MPa, 610 MPa, and 28.4%, respectively. Optical microscopy, scanning electron microscopy （SEM）, and transmission electron microscopy （TEM） were employed to identify the microstructures of the TRIP steels. The final microstructures consist of ferrite, bainite, and retained austenite. The results of quantitative color metallography show that the fraction of the retained austenite is about 5.8%.     

Effect of Stirring Velocity in Micro Fused-Casting for Metal on Microstructure and Mechanical Properties of A356 Aluminum Alloy Slurry

A novel micro fused-casting for metal(MFCM) process for producing A356 aluminum alloy slurry was proposed. MFCM means that the refined metal slurry is pressed out from the outlet of bottom of crucible to the horizontal movable plate. With the aid of 3D manufacturing software, the melt is solidified and formed layer by layer. The stirring could keep the ingredients and the heat diffusion of metal slurry uniform in the crucible due to the shear force breaking down the dendrite arms. The solidus and liquidus temperatures of A356 alloy were 559.2 and 626.3 ℃, respectively, which were measured by differential scanning calorimetry(DSC). Effect of different stirring velocities of MFCM on the microstructure and mechanical properties of A356 slurry was investigated with the pouring temperature controlled at 620 ℃. The microstructure and mechanical performance were the best when the stirring velocity was 1 200 r/min in MFCM. The microstructures of the A356 aluminum alloy slurry were mainly composed of fine spherical or rose grains. The average roundness and average grain size reached 2.2 and 41 μm and the tensile strength of A356 alloy slurry reached 207.8 MPa, while the average vickers hardness was 81.1 HV.     

Rheo-diecasting Process for Semi-solid Aluminum Alloys

A novel one-step semisolid processing technique, the rheo-diecasting （RDC） process, was developed, which adapts in situ creation of semisolid metal slurry with fine and spherical solid particles followed by direct shaping of the slurry into a near-net shape component using the existing cold chamber diecasting process. The RDC process was applied to process A356 and A380 aluminum alloys. The resulting microstructures and mechanical properties of RDC products under as-cast and various heat treatment conditions were analyzed. The experimental results show that the RDC samples have an extremely low porosity, a fine and uniform microstructure throughout entire casting, and consequently much improved strength and ductility in the as-cast condition. The strength of RDC A356 alloy can be substantially improved under T5 and T6 heat treatments without loss of ductility.     

Effects of annealing on microstructure, mechanical and electrical properties of AlCrCuFeMnTi high entropy alloy

The multi-component A1CrCuFeMnTi high entropy alloy was prepared using a vacuum arc melting process. Serial annealing processes were subsequently performed at 590 ℃, 750 ℃, 955 ℃ and 1 100 ℃ respectively with a holding time of 4 h at each temperature. The effects of annealing on microstructure, mechanical and electrical properties of as-cast alloy were investigated by using differential thermal analysis （DTA）, X-ray diffraction （XRD）, scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. The experimental results show that two C14 hexagonal structures remain unchanged after annealing the as-cast A1CrCuFeMnTi alloy specimens being heated to 1 100℃. Both annealed and as-cast microstructures show typical cast-dendrite morphology and similar elemental segregation. The hardness of alloys declines as the annealing temperature increases while the strength of as-cast alloy improves obviously by the annealing treatment. The electrical conductivities of annealed and as-cast alloys are influenced by the distribution of interdendrite re~ions which is rich in Cu element.     

In situ fabrication and properties of AlN dispersion strengthened 2024 aluminum alloy

Nanoscaled aluminum nitride （AlN） dispersion strengthened 2024 aluminum alloy was fabricated using a novel approach in which Al-Mg-Cu compacts were partially nitrided in flowing nitrogen gas. The compacts were subsequently consolidated by sintering and hot extrusion. The microstructure and mechanical properties of the material were preliminarily investigated. Transmission electron microscopy and X-ray diffraction results revealed that AlN particles were generated by the nitridation of Al-Mg-Cu compacts. The material exhibited excellent mechanical properties after hot extrusion and heat treatment. The ultimate tensile and yield strengths of the extruded samples containing 8.92vol% AlN with the T6 heat treatment were 675 and 573 MPa, respectively.     

Microstructure and mechanical properties of AZ91 magnesium alloy subject to deep cryogenic treatments

AZ91 magnesium alloy was subjected to a deep cryogenic treatment. X-ray diffraction （XRD）, scanning electronic microscopy （SEM）, and transmission electronic microscopy （TEM） methods were utilized to characterize the composition and microstructure of the treated samples. The results show that after two cryogenic treatments, the quantity of the precipitate hardening β phase increases, and the sizes of the precipitates are refined from 8-10μm to 2-4μm. This is expected to be due to the decreased solubility of aluminum in the matrix at low temperature and the significant plastic deformation owing to internal differences in thermal contraction between phases and grains. The polycrystalline matrix is also noticeably refined, with the sizes of the subsequent nanocrystalline grains in the range of 50-100 nm. High density dislocations are observed to pile up at the grain boundaries, inducing the dynamic recrystallization of the microstructure, leading to the generation of a nanocrystalline grain structure. After two deep cryogenic treatments, the tensile strength and elongation are found to be substantially increased, rising from 243 MPa and 4.4% of as-cast state to 299 MPa and 5.1%.     

Effect of ECAP on the Microstructure and Mechanical Properties of a High-Mg_2Si Content Al-Mg-Si Alloy

A high-Mg2Si content Al alloy was extruded by equal channel angular pressing(ECAP) for 8 passes at 250 ℃ and an ultrafine-grained structure with an average grain size of about 1.5 μm was achieved.The coarse skeleton-shaped Mg2Si phase presenting in the as-cast alloy are significantly fragmented into fine rod-shaped as well as equiaxed particles mostly less than about 230 nm and become relatively dispersed.The tensile strength 192.8 MPa and the elongation up to 31.3% at ambient temperature are attained in the 8-pass ECAPed alloy versus 163.3 MPa and 9.1% in the as-cast alloy.High-temperature creep test at 250 ℃ reveals that the ECAPed sample exhibits a high elongation close to 100% at a relatively high creep rate 7.64×10-5 s-1,compared to the elongation 56% at a low strain rate 1.74×10-7 s-1 in the as-cast alloy.     

钢丝增强AZ91复合材料的力学性能

为了提高AZ91镁合金的力学性能,采用浸入铸造法制备了体积分数为3.3%的不锈钢纤维增强AZ91复合材料,并在相同条件下对AZ91及其复合材料进行了热挤压处理.采用扫描电镜（SEM）和力学性能试验机分别对铸态和挤压态材料的显微组织、断口和拉伸性能进行了研究.结果表明：铸态AZ91及其复合材料的抗拉强度分别为250和240MPa.然而经过挤压后,钢丝增强AZ91镁合金的屈服强度和抗拉强度分别达到了375和428.6MPa,与挤压态AZ91和铸态AZ91复合材料相比,分别提高了50%、20%和57.6%、78.6%.同时挤压态复合材料的塑性变形量也显著提高.     

Mg-Gd-Er-Zn稀土变形镁合金的微观组织与力学性能

为研究Mg-Gd-Er-Zn稀土变形镁合金微观组织与力学性能,通过金属模铸造、固溶处理、热挤压和时效处理工艺过程,制备了Mg-Gd-Er-Zn稀土变形镁合金,并利用金相显微镜(optical microscopy,OM)、X射线衍射仪(Xray diffraction,XRD)、扫描电镜(scanning electron microscopy,SEM)及透射电镜(transmission electron microscopy,TEM)等手段进行表征.结果表明:Mg-Gd-Er-Zn合金的铸态组织主要由α-Mg基体和沿晶界分布的(Mg,Zn)3Gd第2相组成,固溶后生成层片状的长周期堆垛有序(long period stacking ordered,LPSO)结构;经过热挤压变形,合金的晶粒得到显著细化;时效处理过程中,合金中析出纳米级尺寸的β'相.最终时效态合金的室温抗拉强度、屈服强度和伸长率可分别达397.5 MPa、359.0 MPa和6.0%.     

热处理对2524铝合金显微组织及力学性能影响

在400℃下对铸态2524铝合金进行轧制成形,总变形量为90%,采用光学金相显微镜、拉伸试验机等设备检测轧制板材显微组织及力学性能.研究结果表明：随着固溶温度的升高,Al2Cu,Al2CuMg等第二相粒子数量逐渐减少,在490℃～500℃下基本固溶进铝基体中,其显微硬度值随着固溶温度的升高逐渐增大,当固溶温度为490℃时其显微硬度值为131.4 HV;2524铝合金轧制板材经490℃/20 min＋190℃/22 h处理后,其抗拉强度为485 MPa,延伸率为13.5%.     

Multilayer Clad Plate of Stainless Steel/Aluminum/Aluminum Alloy

The 3, 5, 20 layer clad plate from austenitic stainless steel, pure aluminum and aluminum alloy sheets were fabricated in different ways. The stretch and interface properties were measured. The result shows that 20 layer clad plate is better than the others. Well-bonded clad plate was successfully obtained in the following procedure: Basic clad sheet from 18 layer Al1060/Al3003 sheets was firstly obtained with an initial rolling reduction of 44% at 450 ℃, followed by annealing at 300 ℃, and then with reduction of 50% at 550 ℃ from STS304 on each side. The best 20 layer clad plate was of 129 MPa bonding strength and 225 MPa stretch strength.     

Al-12．7Si-0．7Mg合金脉冲MIG焊接头组织与性能

采用进口ER4047作为填充焊丝对Al-12．7Si-0．7Mg合金热挤压板材实施脉冲MIG直缝对焊．利用金相观察、显微硬度测定及拉伸性能测试等方法研究了焊接接头的显微组织与力学性能．结果表明：利用优化的焊接工艺参数,获得了外观和内部质量良好的焊缝,焊接接头平均抗拉强度为180MPa,达到基材的98％．     

液态模锻6061铝合金轮毂组织及性能

采用液态模锻成型时,为了研究铝合金轮毂不同部位的微观组织和力学性能,利用金相显微镜和拉伸试验机对液态模锻6061铝合金轮毂不同部位的组织及性能进行了研究.结果表明:外轮缘处晶粒最细小,而轮辐部位的晶粒最粗大;外轮缘的抗拉强度和伸长率最高,可以分别达到371 MPa和16%,轮辐部位的抗拉强度强度和伸长率最低,分别为346 MPa和9%.轮辋处的合金晶粒大小不一,且部分晶粒被拉长变形,这是由于该处糊状金属流动产生的冲刷和挤压所致.     

5B01铝合金方管型材的热挤压温度试验

用低倍宏观观察、高倍扫描电镜微观组织观察和断口形貌观察等方法,对5B01铝合金方管型材内外表面、外角、焊缝以及力学拉伸断口进行观察,研究了挤压温度对型材挤压质量的影响。结果表明:该合金在430℃时挤压加工,方管型材的内外表面质量好,外角无裂纹,焊合效果良好,型材整体塑性较好,呈韧性断裂,而且具有较好的基本力学性能,抗拉强度、屈服强度和延伸率分别为335 MPa,138 MPa和26%。     

Squeeze casting of Al-Cu alloy

In order to use the cast method to replace forge method in producing the load-bearing wheel used in certain heavy duty vehicle, simplified and reduced size load-bearing wheels were squeeze cast and studied using Al-Cu alloy. Tensile properties, hardness, microstructures and morphologies of the squeeze-cast wheels were investigated. The results show that the finer microstructure, higher density, strength, toughness and hardness were achieved through the squeeze casting. Ultimate tensile strength of 428 MPa, yield strength of 360 MPa, elongation of 13.1% were achieved for T5 heat-treated squeeze-cast wheels. The Brinell hardness of squeeze-cast wheels is from HB 120 to HB 137.     

Microstructure and mechanical properties of ultrafine grained Mg15Al alloy processed by equal-channel angular pressing

An as-cast magnesium alloy with high Al content Mg15Al was subjected to equal-channel angular pressing (ECAP) through a die with an angle of ϕ=90° at 553 K following route B_c. It is found that the network β-Mg₁₇Al₁₂ phases in the as-cast Mg15Al alloy are broken into small blocks and dispersed uniformly with increasing numbers of pressing passes. Moreover, many nano-sized Mg₁₇Al₁₂ particles precipitate in the ultra-fine α-Mg matrix. The grains are obviously refined. However, the grain structure is inhomogeneous in different areas of the alloy. The average size of the primary phase α-Mg is reduced to about 1 μm while grains of around 0.1–0.2 μm are obtained in some two-phase areas. With additional ECAP passes (up to 8), coarsening of the grains occurs by dynamic recovery. Room temperature tensile tests show that the mechanical properties of Mg15Al alloys are markedly improved after 4 ECAP passes. The ultimate tensile strength and elongation to failure increase from 150 MPa to 269.3 MPa and from 0.05% to 7.4%, respectively. Compared with that after 4 passes, the elongation to failure of the alloy increases but the strength of the alloy slightly decreases after 8 ECAP passes. Fracture morphology of the ECAP-processed alloy exhibits dimple-like fracture characteristics while the as-cast alloy shows quasi-cleavage fractures.