Microstructure and mechanical properties of Al-12Si and Al-3.5Cu-1.5Mg-1Si bimetal fabricated by selective laser melting

An Al-12 Si/Al-3.5 Cu-1.5 Mg-1 Si bimetal with a good interface was successfully produced by selective laser melting(SLM).The SLM bimetal exhibits four successive zones along the building direction:an Al-12 Si zone,an interfacial zone,a texture-strengthening zone and an Al-Cu-Mg-Si zone.The interfacial zone(<0.2 mm thick)displays an increasing size of the cells composed of eutectic Al-Si and a discontinuous cellular microstructure,resulting in the lowest hardness of the four zones.The texturestrengthening zone(around 0.3 mm thick)shows a remarkable variation of the hardness and<001>fiber texture.Electron backscatter diffraction analysis shows that the grains grow gradually from the interfacial zone to the Al-Cu-Mg-Si zone along the building direction.Additionally,a strong<001>fiber texture develops at the Al-Cu-Mg-Si side of the interfacial zone and disappears gradually along the building direction.The bimetal exhibits a room temperature yield strength of 267±10 MPa and an ultimate tensile strength of 369±15 MPa with elongation of 2.6±0.1%,revealing the potential of selective laser melting in manufacturing dissimilar materials.     

Microstructure and mechanical properties of as-cast Mg-4Zn-0.5Zr-0.2Cu-0.2Ce alloy

In this study, an approach is proposed to improve the microstructure and mechanical properties of Mg-4Zn-0.5Zr alloy by combining trace Cu and rare earth Ce addition. The results showed that Cu and Ce additions led to obvious grain refinement and the formation of Mg-Zn-Cu and Mg-Zn-Ce phases. The Mg-Zn-Ce phase was identified to have an orthorhombic structure. The length of the [0001]_α rods in the Cu-containing alloys remarkably decreased. The yield strength increased slightly after Cu and Ce co-addition, which was attributed to grain refinement and precipitation strengthening. The coarse Mg-Zn-Ce phase distributed at the grain boundaries would reduce the ductility by promoting crack propagation during tensile processes.     

Effect of minor content of Gd on the mechanical and degradable properties of as-cast Mg-2Zn-xGd-0.5Zr alloys

RE-containing Mg alloys used as biodegradable medical implants exhibit good promising application due to their good mechanical properties and degradation resistance. In this work, effect of Gd on the microstructure, mechanical properties and biodegradation of as-cast Mg-2Zn-xGd-0.5Zr alloys was investigated. The results showed that there were mainly α-Mg, I-phase, W-phase and MgZn2 phase in Mg-Zn-Gd-Zr alloys. With increase of the Gd content, the strength of the alloys was enhanced due to the second phase strengthening and grain refinement. The degradation resistance of Mg-2Zn-0.5Zr alloy was increased by adding 0.5%–1% Gd due to the uniformly distributed second phases which acted as a barrier to prevent the pitting corrosion. However, increasing Gd content to 2% reduced the degradation resistance of the alloy due to the galvanic corrosion between the matrix and the second phases.The good degradation resistance and mechanical properties of as-cast Mg-2Zn-1Gd-0.5Zr alloy makes it outstanding for biomaterial application.     

Effects of Fe concentration on microstructure and corrosion of Mg-6Al-1Zn-xFe alloys for fracturing balls applications

Mg-6Al-1Zn-xFe (x = 0, 1, 3, 5 and 7 wt%) alloys were prepared by powder metallurgy and followed by hot extrusion. Majority of Fe element exists as insoluble particles in the alloys. The as-extruded alloys showed higher degradable rates but less stable mechanical properties than as-annealed alloys. Corrosion rate of all the alloys increased with increasing Fe concentration, reaching 2.4 mL cm⁻² h^-1. 0.2% yield strength of all the alloys was higher than 150 MPa. In short, Mg-6Al-1Zn-xFe alloys have an attractive combination of corrosion and mechanical properties, which holds a bright future for fracturing balls applications.     

Investigation on microstructure and mechanical properties of Ti14 alloy after semisolid deformation

Abstract

This study details the development of microstructure of Ti14 alloy as a function of the forging temperature and forging ratio in semisolid state and influence of resulting microstructure on the mechanical properties. The results reveal that dynamic recrystallisation occurred during semisolid forging, and the grain refinement was attained. Grain size increased in the forging temperature and decreased in the forging ratio. High ultimate tensile strengths and low elongation have been achieved after semisolid forging. The strength decreased with increasing forging temperature, while the ductility increased with increasing forging ratio. The relative contributions of tensile properties were attributed to the varieties of grain size obtained by thixoforging.     

Structural, microchemistry, and hydrogenation properties of TiMn0.4Fe0.2V0.4, TiMn0.1Fe0.2V0.7 and Ti0.4Zr0.6Mn0.4Fe0.2V0.4 metal hydrides

In this work, TiFe-based alloys have been developed according to the stoichiometry Ti1-xAx Fe1-yBy (A [triple bond] Zr; B [triple bond] Mn, V). The hydrogen solubility properties have been investigated to develop dynamic hydrides of Ti-based alloys for hydrogen storage applications. The hydrogenation behavior of these alloys has been studied, and their hydrogen storage capacities and kinetics have been evaluated. Several activation modes, including activation at high temperatures under hydrogen pressure, have been attempted for the as-milled powders. In order to clarify the structural/microstructural characteristics, and chemical composition before and after hydrogenation, X-Ray Diffraction (XRD), EDAX-Mapping Analysis and Scanning Electron Microscopy (SEM), have been carried out for the samples. Modeling of the isotherms has been performed by using MATLAB programming. The maximum gravimetric density of 4.3 wt%, has been obtained on the sample with the BCC main phase. The calculated enthalpy of reaction (deltaH) is found to be about 4 kJ/mol.     

Effects of heat treatments on the microstructures and mechanical properties of Mg–3Nd–0.2Zn–0.4Zr (wt.%) alloy

Microstructure and mechanical properties of as-cast and different heat treated Mg–3Nd–0.2Zn–0.4Zr (wt.%) (NZ30K) alloys were investigated. The as-cast alloy was comprised of magnesium matrix and Mg₁₂Nd eutectic compounds. After solution treatment at 540 °C for 6 h, the eutectic compounds dissolved into the matrix and small Zr-containing particles precipitated at grain interiors. Further aging at low temperatures led to plate-shaped metastable precipitates, which strengthened the alloy. Peak-aged at 200 °C for 10–16 h, fine β″ particles with DO₁₉ structure was the dominant strengthening phase. The alloy had ultimate tensile strength (UTS) and elongation of 300–305 MPa and 11%, respectively. Aged at 250 °C for 10 h, coarse β′ particles with fcc structure was the dominant strengthening phase. The alloy showed UTS and elongation of 265 MPa and 20%, respectively. Yield strengths (YS) of these two aged conditions were in the same level, about 140 MPa. Precipitation strengthening was the largest contributor (about 60%) to the strength in these two aged conditions. The hardness of aged NZ30K alloy seemed to correspond to UTS not YS.     

Microstructure and mechanical properties of Mg-4.0Zn-0.5Ca alloy

A new kind of Mg-4.0 wt.%Zn-0.5 wt.%Ca alloy is fabricated by casting and hot extrusion for used as a high performance structure material as well as a biomaterial. In the as-cast alloy, the average grain size of the α-Mg is 120-150 µm and the precipitated second phases are distributed uniformly in α-Mg grains. The as-cast Mg-4.0 wt.%Zn-0.5 wt.%Ca alloy shows a good balance between the tensile strength (211 MPa) and ductility (17% in elongation). After hot extrusion at 593 K, the second phase is greatly refined and the average grain size of the α-Mg is reduced to 8-12 μm which is resulted from dynamic re-crystallization during hot extrusion. In this case, it exhibits a high tensile strength (273 MPa) and a high ductility (34% in elongation) at room temperature.     

Effects of Sc Addition and Annealing Treatment on the Microstructure and Mechanical Properties of the As-rolled Mg-3Li alloy

The microstructures and mechanical properties of the as-rolled Mg-3Li and Mg-3Li-1Sc (wt%) alloys before and after annealing treatment have been investigated. Results show that the grains are refined evidently and the recrystallization temperature is improved for more than 100°C by adding 1 wt% Sc into the Mg-3Li alloy. After complete recrystallization, both the strength and ductility of the Mg-3Li alloy are improved evidently with the addition of minor Sc. The brittle fracture tendency of Mg-3Li-1Sc alloy also reduces obviously.     

复合微合金化对Al-Mg合金组织与性能的影响

研究了Sc和Ti复合微合金化对Al-Mg合金显微组织与拉伸性能的影响.结果表明:Sc和Ti复合微合金化可以显著提高Al-Mg合金的强度,并可细化铸态合金的晶粒组织.微量Sc和Ti的加入可使合金中形成大量细小弥散的球形Al3(Ti,Sc)粒子,这些Al3(Ti,Sc)粒子对位错和亚晶界具有强烈地钉扎作用,因而能强烈抑制合金的再结晶.Sc和Ti复合微合金化的Al-Mg合金的强化作用主要来源于Al3(Ti,Sc)粒子的析出强化和亚结构强化以及细晶强化.     

Effects of calcium on the microstructures and tensile properties of Mg-5Li-3Al alloys

The as-cast Mg-5Li-3Al-xCa (x = 0, 0.5, 1, 1.5 wt.%) was prepared with vacuum induction melting furnace, then processed by hot extrusion. The microstructures and tensile properties were investigated. The results show that the grains of as-cast alloys were refined gradually with the increase of Ca content from 0.5 wt.% to 1 wt.%, while the Ca content increases to 1.5 wt.%, the grain size increases. The microstructures of investigated alloys were further refined after hot extrusion. Both as-cast and as-extruded Mg-5Li-3Al-0.5Ca alloys have the highest mechanical properties, which is mainly attributed to the grain refinement caused by the addition of Ca and the formation of strengthening phase, Al₄Ca. When the addition of Ca is up to 1-1.5 wt.%, the tensile properties of alloys are worsened due to the excessive (Mg, Al)₂Ca eutectic phase forming at grain boundary.     

Microstructural evolution and mechanical properties of Mg-9.8Gd-2.7Y-0.4Zr alloy produced by repetitive upsetting

A newly developed severe plastic deformation(SPD) technique, i.e. repetitive upsetting(RU), is employed to improve the strength and ductility of a Mg-Gd-Y-Zr alloy. During the RU processing, dynamic recrystallization occurs in the Mg alloy, which leads to a significant grain refinement from 11.2 μm to 2.8 μm.The yield strength(YS), ultimate tensile strength(UTS) and elongation increase simultaneously with increasing RU passes. The microstructural evolution is affected by processing temperatures. Dynamic recrystallization prevails at low temperatures, while dynamic recovery is the main effect factor at high temperatures. Texture characteristics gradually become random during multiple passes of RU processing,which reduces the tension-compression asymmetry of the Mg-Gd-Y-Zr alloy.     

Effect of melt treatment on microstructure and impact properties of Al-7Si and Al-7Si-2.5Cu cast alloys

The microstructures and impact toughness of Al-7Si and Al-7Si-2.5Cu cast alloys were studied after various melt treatments like grain refinement and modification. The results indicate that combined grain refined and modified Al-7Si-2.5Cu alloys have microstructures consisting of uniformly distributed α-Al grains, interdendritic network of fine eutectic silicon and fine CuAl₂ particles in the interdendritic region. These alloys exhibited improved impact toughness in as cast condition when compared to those treated by individual addition of grain refiner or modifier. The improved impact toughness of Al-7Si-2.5Cu alloys are related to breakage of the large aluminum grains and uniform distribution of eutectic silicon and fine CuAl₂ particles in the interdendritic region resulting from combined refinement and modification. This paper attempts to investigate the influence of microstructural changes in the Al-7Si and Al-7Si-2.5Cu cast alloys by grain refinement, modification and combined action of both on the impact toughness.     

Effect of Zr on the microstructure, mechanical properties and corrosion resistance of Mg–10Gd–3Y magnesium alloy

The influence of Zr on the microstructure, mechanical properties and corrosion resistance of Mg–10Gd–3Y (wt.%) magnesium alloy was investigated. The grain size of alloys decreased with Zr content from 0% to 0.93% (wt.%). The addition of Zr greatly improved the ultimate tensile strength (UTS) and the elongation (EL), while slightly improved the tensile yield strength (TYS). The UTS and the EL of the alloy containing 0.93% Zr increased by 125.8 MPa and 6.96% compared with base alloy, respectively. The corrosion resistances were found to decrease with Zr content from 0% to 0.42% and then increase from 0.42% to 0.93%. The differences in the sizes and distributions of the Zr-rich particles have significant effects on the corrosion behaviors. The alloy with 0.42% Zr addition revealed the optimum combination of mechanical properties and corrosion resistance.     

Influence of oxygen content on the microstructure and mechanical properties of cold rolled Ti-32.5Nb-6.8Zr-2.7Sn-xO alloys after aging treatment

The influence of oxygen (O) content on the microstructure and mechanical properties of cold rolled Ti-32.5Nb-6.8Zr-2.7Sn-xO (TNZS-xO; x?=?0, 0.3, 0.6; mass%) alloys after aging at temperature range from 350 to 600?°C for 24?h was investigated. Results showed that the cold rolled TNZS-xO alloys possess single β phase. During the aging process, O could not only effectively suppress the precipitation of ω phase but also retard the formation and decomposition of α phase. In addition, the corresponding temperatures of the maximal volume fraction of α phase precipitation and the (α+β)/β transus temperatures of the TNZS-xO alloys were all increased with the increasing of O content. For mechanical properties, it was found that the strength and Young's modulus of the TNZS-xO alloys increased owing to the ω phase and/or α phase precipitation and decreased owing to the α phase decomposition. However, the elongation showed the opposite change tendency with the above mentioned strength. The mechanical properties of TNZS-xO alloys can be controlled over a wide range by subjecting to aging treatment and/or changing their O content. When aged at or below 450?°C, the TNZS-xO alloys exhibit great potential to become a series of new candidates for biomedical applications since they possess high strength (870–1460?MPa), low Young's modulus (45.1–75.6?GPa), high strength-to-modulus ratio (0.018–0.02) and appropriate elongation (7.2%–14.9%), which are superior to those of Ti-6Al–4?V alloy and suitable for the use as bio-implant materials.     

Effects of Sn addition on as-cast microstructure, mechanical properties and casting fluidity of ZA84 magnesium alloy

The effects of Sn addition on the as-cast microstructure, mechanical properties and casting fluidity of the ZA84 magnesium alloy are investigated. The results indicate that adding 0.5–2.0 wt.%Sn to the ZA84 alloy not only can result in the formation of Mg₂Sn phase but also can refine the Mg₃₂(Al, Zn)₄₉ phase and suppress the formation of Mg₃₂(Al, Zn)₄₉ phase, and with the increase of Sn amount from 0.5 wt.% to 2.0 wt.%, the morphology of Mg₃₂(Al, Zn)₄₉ phase gradually changes from coarse continuous and/or quasi-continuous net to relatively fine quasi-continuous and/or disconnected shapes. In addition, adding 0.5–2.0 wt.%Sn to the ZA84 alloy can improve the tensile and creep properties, and casting fluidity of the alloy. Among the Sn-containing ZA84 alloys, the ZA84 alloy added 1.0 wt.%Sn exhibits the best ultimate tensile strength, elongation and casting fluidity while the ZA84 alloy added 2.0 wt.%Sn has the best yield strength and creep properties.     

Effects of Zn on the microstructure, mechanical properties, and damping capacity of Mg-Zn-Y-Zr alloys

The influences of Zn on the microstructure, mechanical properties, and damping capacity of as-extruded (Mg-5%Y-0.6%Zr)_1−xZn_x (x = 2%, 4%, 6%, mass fraction) alloys were investigated by optical microscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, tensile testing, and dynamic mechanical analysis (DMA). The phase composition and microstructure of the alloys displayed evident variations with changes in Zn content. When the mass fraction of Zn changed from 2% to 6%, the phases mainly consisted of a long period stacking ordered (LPSO) X-phase (Mg₁₂YZn) and a W-phase (Mg₃Y₂Zn₃). Comparison of the mechanical properties and damping capacities of the different phases showed that the X-phase benefits the mechanical properties of the alloy without drastic impairment to their damping capacities. The damping capacities are discussed in terms of the Granato-Lücke theory and G-L plots.     

Effects of volume ratio on the microstructure and mechanical properties of particle reinforced magnesium matrix composite

In the present study, the AZ91 alloy reinforced by (submicron + micron) SiCp with four kind volume ratio was fabricated by the semisolid stirring casting technology. The influence of volume ratio between submicron and micron SiCp on the microstructure and mechanical properties of Mg matrix was investigated. Results show that the submicron SiCp is more conducive to grain refinement as compared with micron SiCp. With the increase of volume ratio, the submicron particle dense regions increase and the average grain size decreases. The yield strength of bimodal size SiCp/AZ91 composite is higher than monolithic micron SiCp/AZ91composite. Both Δσ_Hall–Petch and Δσ_CTE increase as the volume ratio changes from 0:10, 0.5:9.5, 1:9 to 1.5:8.5. Among the composite with different volume ratio, the S-1.5 + 10-8.5 composite has the best mechanical properties. The interface debonding is found at the interface of micron SiCp-Mg. As the increase of volume ratio, the phenomenon of interface debonding weakens and the amount of dimples increases.     

Microstructural evolution,dislocation density and tensile properties of Al-6.5Si-2.1Cu-0.35Mg alloy produced by different casting processes

Al-Si-Cu-Mg foundry alloys are used in casting process technologies.However,their strength proper-ties remain low due to their microstructural characteristics and porosity.In this work,the microstruc-tural characteristics,dislocation densities,and mechanical properties of Al-Si-Cu-Mg cast alloys prepared through different casting methods were studied experimentally.Four casting processes,namely,gravity casting (GC),rheocasting (RC),thixoforming (Thixo),and Thixo with heat treatment,were used.The GC and RC samples had mainly dendritic α-Al phase microstructures and exhibited coarse Si particles and intermetallic compounds in their interdendritic regions.By contrast,the Thixo and heat-treated Thixo(HT-Thixo) samples exhibited microstructural refinement with uniformly distributed α-Al globules,fine fibrous Si particles,and fragmented intermetallic compounds among α-Al globules.The accumulation of dislocation densities increased in the Thixo sample as the strain was increased due to plastic deforma-tion.Furthermore,the ultimate tensile strength and yield strength of the HT-Thixo sample increased by 87％ and 63％,respectively,relative to those of the GC sample.The cleavage fracture displayed by the GC and RC samples led to brittle failure.Meanwhile,the Thixo and HT-Thixo samples presented dimple-based ductile fracture.