Preparation for Semi-Solid Aluminum Alloy Slurry under Weak Electromagnetic Stirring Conditions

The effects of pouring temperature, short electromagnetic stirring with low strength and then soaking treatment on the microstructure of AISi7Mg alloy were investigated. The results show that if AlSi7Mg alloy is poured at 630 or 650℃ and meanwhile stirred by an electromagnetic field at a low power for a short time, the pouring process can be easily controlled and most solidified primary α-Al grains become spherical and only a few of them are rosette-like. Weak electromagnetic stirring makes the temperature field more homogeneous and makes the primary α-Al grains disperse in a larger region, which leads to the spherical microstructures of primary α-Al grains. When the AISi7Mg alloy is soaked or reheated at the semisolid state, the primary α-Al grains ripen further and they become more spherical, which is favorable to the semi-solid forming of AlSi7Mg alloy.     

电磁搅拌对半固态AZ91D镁合金组织的影响

研究了电磁搅拌参数对连续冷却条件下AZ91D镁合金组织的影响.结果表明:当电磁搅拌的频率达到或高于50 Hz时,半固态AZ91D镁合金浆料或坯料组织中的球状初生固相越来越多,越来越圆整;在电磁搅拌频率为200 Hz和冷却速率较低的条件下,搅拌的功率越大,半固态AZ91D镁合金组织中的球状初生固相越多,晶粒也越细小.在电磁搅拌条件下,AZ91D镁合金熔体的激烈流动导致较为均匀的温度场和溶质场、更加剧烈的温度起伏,促进了半固态AZ91D镁合金球状组织的形成.半固态重熔加热使半固态AZ91D镁合金坯料初生固相的形态发生进一步的球化.     

The formation mechanism of non-dendritic primary α–Al phase in semi-solid AlSi7Mg Alloy

In this paper, a process to make non-dendritic semi-solid AlSi₇Mg alloy by electromagnetic stirring and the temperature field of the stirred melt cooled is continuously investigated. It is proposed that a new kinetic factor for primary α-Al nucleation is that alow thermal gradient exists in the electromagnetically stirred melt, for which the primary dendrite arms and secondary dendrite arms are refined. The results also show that the root remelting of the secondary dendrite arms is an important mechanism of the primary α-Al refinement. Strong electromagnetic stirring greatly reduces the composition supercooling in the melt and eliminates the preferred growth of primary dendrite arms, therefore, many rosettes or spherical primary α-Al phase particles form finally.     

The formation mechanism of non-dendritic primary α-Al phase in semi-solid AlSi7Mg Alloy

In this paper, a process to make non-dendritic semi-solid AlSi₇Mg alloy by electromagnetic stirring and the temperature field of the stirred melt cooled is continuously investigated. It is proposed that a new kinetic factor for primary α-Al nucleation is that a low thermal gradient exists in the electromagnetically stirred melt, for which the primary dendrite arms and secondary dendrite arms are refined. The results also show that the root remelting of the secondary dendrite arms is an important mechanism of the primary α-Al refinement. Strong electromagnetic stirring greatly reduces the composition supercooling in the melt and eliminates the preferred growth of primary dendrite arms, therefore, many rosettes or spherical primary α-Al phase particles form finally.     

Study on Multiple Electromagnetic Continuous Casting of Aluminum Alloy

To obtain semi-solid Al alloy billet with high quality, an investigation was carried out by imposing a multiple magnetic field from the outside of a copper mold in the continuous casting. AISi6Mg2 alloy designed for semi-solid metal （SSM） processing was continuously cast through a submerged entry nozzle under various conditions. Effects of multiple magnetic field on meniscus motion, temperature distribution and billet quality were examined. The experimental results showed that meniscus disturbance caused by electromagnetic stirring could be controlled effectively and the surface quality of semi-solid AI alloy billet was improved greatly, and an uniformly fine, globular microstructure across the transverse section of the billet was achieved by optimizing the distribution of multiple magnetic field.     

退火态激光选区熔化成形AlSi10Mg合金组织与力学性能

AlSi10Mg合金具有高比强度、高耐磨性等优良特点。由于其成分接近共晶点,成形性能良好,被广泛应用于激光选区熔化技术。然而其热处理制度仍然沿用传统铸态合金的热处理规范,影响了其性能的充分发挥。本工作采用激光选区熔化技术制备了AlSi10Mg合金,并研究了沉积态和后续热处理过程中组织演化规律及其对室温力学性能的影响机制。研究发现：沉积态组织由沿沉积方向生长的α-Al柱状枝晶及枝晶间网状Al-Si共晶组成,具有强烈的〈100〉方向织构,沉积层由三部分组成,分别是细晶区、粗晶区及热影响区,抗拉强度389.5 MPa,伸长率4%。退火过程中,共晶Si破碎、球化,基体中过饱和Si不断析出长大。当退火温度从200 ℃提高到500 ℃时,Si颗粒发生Ostwald熟化,平均尺寸增长了23倍。经过300 ℃和500 ℃退火处理后,试样抗拉强度分别为287.0 MPa和268.0 MPa,但伸长率分别提高到10.3%和17.2%。     

The influences of the microstructure morphology of A356 alloy on its rheological behavior in the semi-solid state

In this paper, the rheological behavior of semi-solid A356 alloy with different solid morphology was studied with an improved static shear test method. The results indicated that the rheological behavior of the alloy was significantly influenced by the structural morphology of the alloy. The alloy had quite different rheological properties even though the same fraction of solid existed in the semi-solid state. The rheological behavior of the alloy fitted a five-element model (H₁–[N₁|H₂]–[N₂|S]) for the as-cast microstructure with developed primary (α-Al dendrites, whereas it fitted a six-element model ([H₁|S₁]–[N₁|H₂]–[N₂|S]) for degenerated dendritic or spheroidal primary α-Al, which had been obtained by electromagnetic stirring and spray deposition, respectively. Computation results showed that the deforming capability and shear rate of the semi-solid alloy increased remarkably with the change of primary α-Al from developed dendrites to degenerated dendrites, and then to spheroidal structures. On the other hand, the temperature dependence of the rheological properties of the semi-solid alloy with spheroidal or degenerated dendritic primary α-Al was much less than that with developed primary α-Al dendrites.     

Effects of Cr and Cr/Mn Combined Additions on Semi-Solid Microstructures of Al-Mg-Si Alloys Produced by D-SSF Process

The effects of Cr and Cr/Mn combined additions on the semi-solid microstructure of wrought Al-Mg-Si alloys are investigated.In the Cr-added alloy,the Al-7Cr compound is formed with homogeneously distributed in theα-Al matrix after homogenization.Both of the Al-7Cr andα-Al-（12）Mn3-Si-2 dispersiod particles are found in the homogenized microstructure of the Cr/Mn-added alloy.In the semi-solid microstructures,the smallestα-Al grains are obtained in the 60% cold-rolled alloys.After prolonged holding time,theα-Al grain size of the Cr/Mn-added alloy is smaller than that of the Cr-added alloy.Heavy deformation by cold-rolling accelerates spheroidization of theα-Al grains.The D-SSF process is found to be useful to modify the microstructures of both the Cr-added and Cr/Mn-added Al-Mg-Si alloys.     

Semi–solid thixo-extrusion of AlSi7MgBe alloy

对采用近液相线半连续铸造技术制备的AlSi7MgBe合金坯料进行半固态挤压成形, 通过组织与性能的分析, 研究了AlSi7MgBe合金的半固态挤压成形性. 结果表明: 用近液相线半连续铸造技术制备的AlSi7MgBe合金坯料具有均匀、细小的蔷薇状组织, 在575℃对其二次加热可获得稳定的、适合于半固态触变成形的球化组织, 进行半固态挤压成形可获得表面光洁, 组织细小、分布均匀的成形件, 在540℃固溶5 h然后175℃时效10 h处理, 其抗拉强度为325 MPa, 伸长率为14.6%, 表明具有良好的半固态挤压成形性.     

ZL201合金液相线铸造与二次加热的合金组织

为了研究半固态金属的成型规律,采用电子显微镜及图像分析仪,研究了近液相线半连续铸造ZL201合金的微观组织及其在二次加热过程中的变化.研究表明,在液相线温度下半连续铸造的ZL201合金组织为均匀、细小的蔷薇状组织,晶粒的平均等积圆直径为43.6μm,晶粒平均圆度为1.88.经二次加热后,铸造组织逐渐转变为等轴晶.在620℃下加热20min后,晶粒平均等积圆直径为111μm,晶粒平均圆度1.42.在640℃下加热20min后,晶粒平均等积圆直径为108μm,晶粒平均圆度1.58.研究表明,近液相线半连续铸造可以获得理想的ZL201合金半固态坯料.     

Effect of isothermal ageing on the semi-solid microstructure of rheoprocessed and partially remelted of A390 alloy with 10% Mg addition

The semi-solid microstructure of commercial A390 (Al—17%Si—4.5%Cu—0.5%Mg) hypereutectic Al–Si alloy with an addition of 10% Mg was investigated for two different processing routes: 1) rheocasting after stirring with rotation speed of 260 rpm and 2) partial remelting after fast cooling in a steel mould. The results show that the morphology of α-Al grains becomes globular during isothermal holding time for both cases. However, at the same isothermal condition, the size of the α-Al phase particles for rheocast samples are larger and their morphology are more globular than for the samples examined after the partial remelting process. The microstuctural evolution, size and shape of the primary Mg₂Si as well as the silicon particles during isothermal ageing in the semi-solid region was also investigated for the two processing conditions.     

激光选区熔化纳米SiC/AlSi7Mg复合材料微观组织及力学性能EI北大核心CSCD

采用机械混合法制备纳米SiC/AlSi7Mg混合粉末,利用激光选区熔化技术(selective laser melting,SLM)成形纳米SiC颗粒增强AlSi7Mg复合材料,观察和分析试样的相对密度、物相和微观组织,并测试材料的硬度和拉伸性能。结果表明:SLM成形纳米SiC/AlSi7Mg复合材料试样的相对密度随着扫描速度和扫描间距的增大均呈现先增加后减少的趋势,相对密度最高可达99.75%;试样微观组织与SLM成形铝合金相似,Si相呈网状结构均匀嵌入α-Al基体中,且在Al基体中存在与Si分布相似的纳米SiC团聚物及Mg_(2)Si相;与AlSi7Mg相比,复合材料微观组织由柱状晶转化为等轴晶,且晶粒明显细化(平均晶粒尺寸为1.36μm);由于SiC的加入,产生细晶强化和固溶强化,试样的硬度和强度均明显提高,硬度最高达到137.3HV,抗拉强度达到448.3 MPa,屈服强度达到334.7 MPa,但伸长率下降至3.9%,断裂模式主要为脆性断裂。     

Microstructure evolution and mechanical properties at high temperature of selective laser melted AlSi10Mg

In this study,the microstructure and tensile properties of selective laser melted AlSilOMg at elevated temperature were investigated with focus on the interfacial region.In-situ SEM and in-situ EBSD analysis were proposed to characterize the microstructural evolution with temperature.The as-fabricated AlSilOMg sample presents high tensile strength with the ultimate tensile strength(UTS)of~450 MPa and yield strength(YS)of~300 MPa,which results from the mixed strengthening mechanism among grain boundary,solid solution,dislocation and Orowan looping mechanism.When holding at the temperature below 200℃for 30 min,the micro structure presents little change,and only a slight decrement of yield strength appears due to the relief of the residual stress.However,when the holding temperature further increases to 300℃and 400℃,the coarsening and precipitation of Si particles inα-Al matrix occur obviously,which leads to an obvious decrease of solid solution strength.At the same time,matrix softening and the weakness of dislocation strengthening also play important roles.When the holding temperature reaches to 400℃,the yield strength decreases significantly to about 25 MPa which is very similar to the as-cast Al alloy.This might be concluded that the YS is dominated by the matrix materials.Because the softening mechanism counteracts work hardening,the extremely high elongation occurs.     

Production of SiC particulate reinforced aluminium composites by melt spinning

Melt spinning is successfully used for the preparation of a rapidly solidified SiC particle reinforced AlSi7Mg0.3 alloy. The composites are prepared by introducing SiC particles in a semi-solid matrix slurry (SiC volume fractions up to 0.15, particle size 10 or 20 m). Duralcan material (SiC volume fraction 0.20, particle size 12 m) was also used. After stirring in the semi-solid state the composites are heated above the liquidus temperature and subsequently melt-spun. Featureless, columnar and dendritic zones can be identified in the ribbons. A finer dendritic structure is found around the SiC particles. The SiC particles tend to segregate to the air side of the ribbons and the segregation effect is influenced by particle size and volume fraction. As interface velocities are higher than the critical velocities predicted by models on interface pushing, it is concluded that fluid flow in the melt puddle is responsible for the segregation effect.     

Influence of thermal rate treatment and low temperature pouring on microstructure and tensile properties of AlSi7Mg alloy

The combination of thermal rate treatment and low temperature pouring was proposed in the present work, and the effects of the novel melt thermal treatment on microstructure and tensile properties of AlSi7Mg alloy have been investigated. The grain size and microstructure of AlSi7Mg alloy were examined by optical microscopy (OM) and scanning electron microscopy (SEM). It was found that the grain size obviously reduced and the growth of the columnar dendrites changed into equiaxed ones by low temperature pouring, especially the novel melt thermal treatment, by which a maximum microstructure refining effect could be obtained. The refinement can be attributed to the multiplication of the nuclei in the melt. Furthermore, the morphology of eutectic silicon changed little, but the size of silicon phase was finer due to the refinement of the grain size and higher cooling rate. Because of the refinement of the grain size and eutectic silicon, the tensile properties were improved, and the ultimate tensile strength and elongation increased by 11.7% and 35.3%, respectively.     

Effects of Technical Parameters of Semi-Solid Stirring and Rheo-Rolling on Microstructure of A356–5wt.%B4C Composite Strip

Aluminum boron carbide composite strip was prepared by semi-solid stirring and rheo-rolling, and the effects of process parameters on microstructure of A356–5wt.%B₄C composite strip were studied. The results showed that the distribution of B₄C particles in the matrix became homogeneous, and the average diameter of α-Al and its roundness decreased with the increase of the stirring speed and the stirring time as well as the decrease of the stirring temperature. The average diameter of the primary α-Al grain increased with the increase of the roll speed. When the stirring speed was 500 rpm, the stirring time was 20 min, the stirring temperature was 853 K (580 °C), and the roll speed was 0.2 m/s, the microstructure of A356–5wt.%B₄C composite strip was mainly composed of spherical or rosette α-Al grains, and the distribution of B₄C particles was homogeneous. The hardness of A356–5wt.%B₄C composite strip was 98 HV, and the ultimate tensile strength and elongation were 186 MPa and 1.8%, respectively. The hardness was improved by 25% comparing with casting alloy A356. The ultimate tensile strength and elongation were improved, respectively, by 28.3% and 5.9%.     

Study of Microstructure Evolution during Semi-Solid Processing of an In-Situ Al Alloy Composite

In the present work, effect of pouring temperature (650°C, 655°C, and 660°C) on semi-solid microstructure evolution of in-situ magnesium silicide (Mg₂Si) reinforced aluminum (Al) alloy composite has been studied. The shear force exerted by the cooling slope during gravity driven flow of the melt facilitates the formation of near spherical primary Mg₂Si and primary Al grains. Shear driven melt flow along the cooling slope and grain fragmentation have been identified as the responsible mechanisms for refinement of primary Mg₂Si and Al grains with improved sphericity. Results show that, while flowing down the cooling slope, morphology of primary Mg₂Si and primary Al transformed gradually from coarse dendritic to mixture of near spherical particles, rosettes, and degenerated dendrites. In terms of minimum grain size and maximum sphericity, 650°C has been identified as the ideal pouring temperature for the cooling slope semi-solid processing of present Al alloy composite. Formation of spheroidal grains with homogeneous distribution of reinforcing phase (Mg₂Si) improves the isotropic property of the said composite, which is desirable in most of the engineering applications.     

Influence of Solid Fraction Casting on Microstructure of Aluminum Alloy 6061

Semi-solid processing of AA6061 alloy near liquidus temperature with the addition of micro- and nanoparticles of same alloy may be highly attractive for small intricate shapes due to excellent mechanical properties. The present work utilizes semi-solid behavior of AA6061 alloy, which reduces macro- and nanosegregation of particles, porosity, and forming forces during the shaping process. The experiment utilizes the semi-solid slurry of different solid fractions mixed with a melt at pouring temperature range of 400 ? 640°C. The potential of solid fraction to produce semi-solid slurry has been investigated with the help of microstructure analysis, which is a crucial need for aluminum industries. The result shows that during the stirring, every dendrite modified itself to fine solid grains and dispersion of these grains takes place inside the molten metal. Alloy cooled directly from semi-solid state results in higher relative density with respect to conventional casting. With increase of solid fraction to 25%, the un-melted solid structure inside the pores and cavities in the direction of elongated grains results in the subsequent enhancement in the impact strength, hardness, and compressive strength as 19 kJ/m², 93 BHN, and 550 MPa, respectively, without any alteration in the basic metal matrix composite.     

纳米WC增强选区激光熔化AlSi10Mg显微组织与力学性能EI北大核心CSCD

为了进一步增强选区激光熔化(SLM)成型AlSi10Mg合金的性能,采用物理混合方法混合纳米WC与AlSi10Mg得到WC质量分数为0.1%的WC/AlSi10Mg复合材料,利用选区激光熔化成型机制备试样块。通过对比同种工艺制备的AlSi10Mg试样,探究纳米WC对其微观组织形成、演变规律及其组织对力学性能的影响。结果显示,WC/AlSi10Mg粉末球形度好,粒度分布集中在20~60μm。WC/AlSi10Mg试样致密度达到99%以上,硬度约为158.89HV,相比AlSi10Mg试样增加了14.58%。WC/AlSi10Mg试样组织生长均匀、致密,有明显的熔池线。晶粒内部为α-Al基体,边界为夹杂着WC的共晶Si相。WC/AlSi10Mg试样屈服强度达到337.75 MPa,抗拉强度高达514.00 MPa,伸长率为3.78%,相比同种工艺AlSi10Mg试样分别增加了4.73%,6.25%和35.97%。因此,SLM成型WC/AlSi10Mg纳米复合材料零件相比AlSi10Mg零件具有更好的应用前景。     

Age hardening of laser beam welded aluminium alloy 6082 using scandium containing filler metal

Abstract

Sheet materials, of thickness 2 mm, of the aluminium alloy AlSi1MgMn (6082) in the aging conditions T4 and T6 were laser beam welded with a CO₂ laser using two different filler wires: a relative common filler AlSi7Mg and a new developed scandium-containing filler AlMg7Sc. To check the feasibility of a post-thermal treatment, the aging behaviour of the base material AlSi1MgMn in the conditions T4 and T6, as well as the aging behaviours of the fusion zones AlSi1MgMn/AlSi7Mg and AlSi1MgMn/AlMg7Sc were investigated. For the base material AlSi1MgMn-T4 and the fusion zone AlSi1MgMn/AlSi7Mg, close square butt weld, a similar aging behaviour is found at moderate temperatures and durations. So aluminium welds with almost constant hardness profiles along the base material, heat affected zone, and fusion zone can be produced by post-aging the welded joint. For the base material AlSi1MgMn-T4 and the fusion zone AlSi1MgMn/AlMg7Sc, close square butt weld, the aging behaviour is different. At temperatures and durations necessary to form precipitates in the fusion zone, the base material is overaged. This behaviour could be improved for single V butt welds. A strong influence of the welding parameters on the aging behaviour of the fusion zone is found, because the amount of melted base and filler materials as well as the solidification rate determine the chemical composition and microstructure of the fusion zone in the as welded state.