Microstructures and mechanical properties of Al 2519 matrix composites reinforced with Ti-coated SiC particles

Ti-coated SiC_p particles were developed by vacuum evaporation with Ti to improve the interfacial bonding of SiC_p/Al composites. Ti-coated SiC particles and uncoated SiC particles reinforced Al 2519 matrix composites were prepared by hot pressing, hot extrusion and heat treatment. The influence of Ti coating on microstructure and mechanical properties of the composites was analyzed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results show that the densely deposited Ti coating reacts with SiC particles to form TiC and Ti₅Si₃ phases at the interface. Ti-coated SiC particle reinforced composite exhibits uniformity and compactness compared to the composite reinforced with uncoated SiC particles. The microstructure, relative density and mechanical properties of the composite are significantly improved. When the volume fraction is 15%, the hardness, fracture strain and tensile strength of the SiC_p reinforced Al 2519 composite after Ti plating are optimized, which are HB 138.5, 4.02% and 455 MPa, respectively.     

Fabrication and characterization of Al356/SiCp semisolid composites by injecting SiCp containing composite powders

Al356/5 vol.% SiC_p cast composites were fabricated by the injection of reinforcement particles into the melt in three different forms, i.e. as untreated SiC_p, milled particulate Al-SiC_p composite powder, and milled Al-SiC_p-Mg composite powder. The resultant composite slurries were then cast in the semisolid temperature range of the alloy, upon which the effects of the type of injected powder on the distribution and incorporation of the reinforcement particles, along with the hardness of the cast composites, were investigated. Injection of milled composite powders resulted in considerable improvement in SiC_p wetting as well as the incorporation and distribution of SiC_p in the Al356 matrix alloy. Al356/5 vol.% SiC_p composite with well dispersed reinforcement particles of less than 3 μm average diameter was successfully produced by injecting Al-SiC_p-Mg composite powder into the melt. The best microstructural characteristics in terms of the reinforcement incorporation and distribution, and the highest hardness value of the cast composites, were achieved when magnesium was added through the injected composite powder and not directly into the melt.     

Microstructure and Mechanical Properties of Al356/SiCp Cast Composites Fabricated by a Novel Technique

In this study, SiC_p containing composite powders were used as the reinforcement carrier media for manufacturing cast Al356/5 vol.% SiC_p composites. Untreated SiC_p, milled particulate Al-SiC_p composite powder, and milled particulate Al-SiC_p-Mg composite powder were injected into Al356 melt. The resultant composite slurries were then cast from either a fully liquid state (stir casting) or semisolid state (compocasting). The results revealed that by injection of composite powders, the uniformity of the SiC_p in the Al356 matrix was greatly improved, the particle-free zones in the matrix were disappeared, the SiC particles became smaller, the porosity was decreased, and the matrix microstructure became finer. Compocasting changed the matrix dendritic microstructure to a finer non-dendritic one and also slightly improved the distribution of the SiC_p. Simultaneous utilization of Al-SiC_p-Mg composite powder and compocasting method increased the macro- and micro-hardness, impact energy, bending strength, and bending strain of Al356/SiC_p composite by 35, 63, 20, 20, and 40%, respectively, as compared with those of the composite fabricated by injection of untreated SiC_p and stir casting process.     

Processing and compressive strength of Al–Li–SiCp composites fabricated by a compound billet technique

Al–Li–SiC_p composites were fabricated by a simple and cost effective stir casting technique. A compound billet technique has been developed to overcome the problems encountered during hot extrusion of these composites. After successful fabrication hardness measurement and room temperature compressive test were carried out on 8090 Al and its composites reinforced with 8, 12 and 18 vol.% SiC particles in as extruded and peak aged conditions. The addition of SiC increases the hardness. 0.2% proof stress and compressive strength of Al–Li–8%SiC and Al–Li–12%SiC composites are higher than the unreinforced alloy. In case of the Al–Li–18%SiC composite, the 0.2% proof stress and compressive strength were higher than the unreinforced alloy but lower than those of Al–Li–8%SiC and Al–Li–12%SiC composites. This is attributed to clustering of particles and poor interfacial bonding.     

Using ARB process as a solution for dilemma of Si and SiCp distribution in cast Al-Si/SiCp composites

A major challenge in achieving the best potential of SiC_p-reinforced aluminum composites is to homogeneously disperse SiC particles within the aluminum alloys. The presence of coarse Si fibers with non-uniform distribution in cast Al-Si alloys, which may lead to poor mechanical properties, is another important problem that limits the application of these alloys. In order to eliminate these problems, accumulative roll bonding (ARB) process was used in this study as a very effective method for improving the microstructure and mechanical properties of the Al356/SiC_p composite. It was found that when the number of ARB cycles was increased, the uniformity of the Si and SiC_p in the aluminum matrix improved, the Si particles became finer and more spheroidal, the free zones of Si and SiC particles disappeared, the porosity of composite decreased, the bonding quality between SiC_p and matrix improved, and therefore mechanical properties of the composites were improved. The microstructure of the manufactured Al356/SiC_p composite after six ARB cycles indicated a completely modified structure so that its tensile strength and elongation values reached 318 MPa and 5.9%, which were 3.1 and 3.7 times greater than those of the as-cast composite, respectively.     

Microstructure and grain growth behavior of an aluminum alloy metal matrix composite processed by disintegrated melt deposition

In this study, a silicon-carbide particulate (SiC_p), reinforced aluminum alloy-based, metal-matrix composite was synthesized using disintegrated melt deposition. Microstructural characterization of the disintegrated melt deposition processed composite samples revealed the presence of columnar-equiaxed shaped grain structure, noninterconnected porosity associated with the reinforcing carbide particulates, improved interfacial integrity between the reinforcement and the aluminum alloy matrix coupled, and a near uniform distribution of the reinforcing SiC particulates in the alloy matrix. An examination of grain growth with the objective of delineating the effects of the silicon carbide particulates revealed a diminishing to minimal role of the reinforcing phase with an increase in temperature from 450 to 590 °C.     

Production and mechanical properties of nano SiC particle reinforced Ti–6Al–4V matrix composite

Different mass fractions (0, 5%, 10%, and 15%) of the synthesized nano SiC particles reinforced Ti–6Al–4V (Ti64) alloy metal matrix composites (MMCs) were successfully fabricated by the powder metallurgy method. The effects of addition of SiC particle on the mechanical properties of the composites such as hardness and compressive strength were investigated. The optimum density (93.33%) was obtained at the compaction pressure of 6.035 MPa. Scanning electron microscopic (SEM) observations of the microstructures revealed that the wettability and the bonding force were improved in Ti64 alloy/5% nano SiC_p composites. The effect of nano SiC_p content in Ti64 alloy/SiC_p matrix composite on phase formation was investigated by X-ray diffraction. The correlation between mechanical parameter and phase formation was analyzed. The new phase of brittle interfaced reaction formed in the 10% and 15% SiC_p composite specimens and resulted in no beneficial effect on the strength and hardness. The compressive strength and hardness of Ti64 alloy/5% nano SiC_p MMCs showed higher values. Hence, 5% SiC_p can be considered to be the optimal replacement content for the composite.     

Effect of forging temperature on the microstructures and mechanical properties of the SiCp/AZ91 magnesium matrix composite

In this paper, 10 vol. pct SiC_p/AZ91 magnesium matrix composite was fabricated by stir casting technology. The ingots were forged at temperatures of 320, 370 and 420 ℃, respectively. XRD, OM and SEM were used to characterize microstructure of the composites. It was shown that the clusters of particles in the as-cast composite were largely eliminated, and that the tensile strength was improved obviously.     

Cyclic Fatigue Fracture Behavior of Spray-Deposited SiCp/Al-Si Composite

The cyclic fatigue characteristics of spray-deposited SiC_p/Al-Si composite were investigated in comparison with the unreinforced Al-Si alloy. The as-extruded specimens were cyclically deformed with fully reversed loading under a range of total strain amplitudes. The results show that the cyclic response characteristics for the reinforced and unreinforced materials are similar to each other. Both the composite and matrix alloys display cyclic hardening under total strain amplitude of 0.35-0.5%. Otherwise, the composite exhibits higher degree of strain hardening than that of the matrix alloy. Dislocation substructure developed during cyclic deformation was analyzed using transmission electron microscopy. The discrepancy between dislocation substructures obtained from processing compared to its development during cyclic strain loading is thought to give rise to the observed cyclic stress response behavior. Fractographic analysis shows that particle/matrix debonding and particle cracking are the main mechanisms of failure in the SiC particle-reinforced composite.     

Thixoforming of AA 2017 aluminum alloy composites

A comparative evaluation has been carried out on the microstructure of aluminum based SiC and Al₂O₃ particle reinforced composites produced by semi-solid direct squeeze forming of composite powder at temperatures of 635-645 °C. The study is focused on the distribution of the reinforcement and the intermetallic phases, the porosity content, the microstructure of the matrix phase, the interfacial state and mechanical properties. The particle size of the reinforcements, the time of the high-energy ball milling procedure for the fabrication of composite powder and the semi-solid forming temperature had a strong influence on the quality of sample in terms of distribution of reinforcement and interfacial interaction. Ball milling improves the interface formation between reinforcement and matrix and influences the remelting behaviour. Increasing ball milling time and decreasing semi-solid forming temperature with isothermal holding time resulted in relatively homogenous microstructures and in a reduced amount of interaction between SiC and metal matrix. Best results were obtained for 5 vol.% SiC_p composites after 3 h ball milling, semi-solid formed at 635 °C and held for 10 min.     

Process study, microstructure, and matrix cracking of SiC fiber reinforced MoSi2 based composites

SiC fiber reinforced SiAlON-MoSi₂ composites have been manufactured by a concurrent fiber winding and low pressure plasma spraying (LPPS) technique to produce a multilayer, circumferentially fiber reinforced composite ring. The LPPS parameters for SiAlON-MoSi₂ powder were optimized by a two-level experimental design approach followed by further optimization, which provided a smooth sprayed surface, low matrix porosity, and high deposition efficiency. The microstructure of SiAlON-MoSi₂ matrix consisted of a lamellar structure built up of individual splats and a uniform distribution of discontinuous SiAlON splats throughout the MoSi₂ matrix. The spray/wind composites exhibited 2% porosity and well-controlled fiber distribution. High temperature consolidation led to the formation of a thick reaction zone at the fiber-matrix interface by a chemical reaction between C coating and MoSi₂. Matrix cracking occurred in SiC _f (15 vol.%)/MoSi₂ after cooling from 1500 to 25 °C and was attributed to the large tensile residual stresses in the matrix developed on cooling because of coefficient of thermal expansion (CTE) mismatch between matrix and fiber. The addition of 40 vol.% SiAlON into the MoSi₂ effectively eliminated the matrix cracking by reducing the matrix-fiber CTE mismatch. Predictions of matrix cracking stress on the basis of residual stresses in the composites showed that the maximum permissible fiber volume fraction to avoid matrix cracking was 6% for SiC _f /MoSi₂ and 23% for SiC _f /SiAlON(40 vol.%)-MoSi₂.     

Identification of σ and Ω phases in AA2009/SiC composites

The microstructure evolution during ageing treatment at 170 and 190 °C of AA2009/SiC composites, reinforced with 15 vol.% particulates and whiskers, was studied by transmission electron microscopy. Besides θ′ and S′ phases, the typical hardening precipitates on Al–Cu–Mg alloys, it was found the presence of Ω and σ (Al₅Cu₆Mg₂) phases in the matrix. σ phase was only found in the matrix of particulate composite, while Ω phase appeared in both. This phase has not been previously observed in Al matrix composites based on conventional Al–Cu–Mg alloys.     

Effects of SiC Volume Fraction and Particle Size on the Deposition Behavior and Mechanical Properties of Cold-Sprayed AZ91D/SiCp Composite Coatings

AZ91D/SiC_p composite coatings were fabricated on AZ31 magnesium alloy substrates using cold spraying. The effects of SiC volume fraction and particle size on the deposition behavior, microhardness, and bonding strength of coatings were studied. The mean sizes of SiC particles tested were 4, 14, and 27 μm. The results show that fine SiC particles (d _0.5 = 4 μm) are difficult to be deposited due to the bow shock effect. The volume fraction of SiC particles in composite coatings increases with the increasing SiC particle size. The microhardness and bonding strength of composite coatings also show increases compared with AZ91D coatings. The volume fractions of SiC particles in the original powder were set at 15, 30, 45, and 60 vol.%. The corresponding contents in composite coatings are increased to 19, 27, 37, and 51 vol.%, respectively. The microhardness of composite coatings also increases as the volume fraction of SiC particles increases.     

Mechanical Behavior of a Magnesium Alloy Nanocomposite Under Conditions of Static Tension and Dynamic Fatigue

In this paper, the intrinsic influence of nano-alumina particulate (Al₂O_3p) reinforcements on microstructure, microhardness, tensile properties, tensile fracture, cyclic stress-controlled fatigue, and final fracture behavior of a magnesium alloy is presented and discussed. The unreinforced magnesium alloy (AZ31) and the reinforced composite counterpart (AZ31/1.5 vol.% Al₂O₃) were manufactured by solidification processing followed by hot extrusion. The elastic modulus, yield strength, and tensile strength of the nanoparticle-reinforced magnesium alloy were noticeably higher than the unreinforced counterpart. The ductility, quantified by elongation-to-failure, of the composite was observably lower than the unreinforced monolithic counterpart (AZ31). The nanoparticle-reinforced composite revealed improved cyclic fatigue resistance over the entire range of maximum stress at both the tested load ratios. Under conditions of fully reversed loading (R = ?1) both materials showed observable degradation in behavior quantified in terms of cyclic fatigue life. The conjoint influence of reinforcement, processing, intrinsic microstructural features and loading condition on final fracture behavior is presented and discussed.     

Magnesium matrix nanocomposites fabricated by ultrasonic assisted casting

Abstract

Magnesium matrix composites reinforced with nano-sized SiC particles (n-SiC_p/AZ91D) were fabricated by high intensity ultrasonic assisted casting. The microstructure of the nanocomposites was investigated by optical microscopy, scanning electronic microscopy (SEM), high resolution transmission electronic microscopy (HRTEM) and Energy Dispersive Spectroscopy (EDS) methods. The results showed that the dispersion and distribution of n-SiC_p in magnesium alloy melts were significantly improved by ultrasonic processing. Compared to the unreinforced AZ91D matrix, mechanical properties of the nanocomposites including tensile and yield strengths were remarkably improved and the yield strength increased by 117% after gravity permanent mould casting.     

Oxidation of ZC63 Mg alloys reinforced with SiC particles between 390 °C and 500 °C in air

The ZC63 magnesium alloys reinforced with 10 wt.% of SiC particles with an average particle size of 50 μm were cast. The fabricated SiC_p/ZC63 composite consisted of an α-Mg matrix, unreacted α-SiC particles, and an intergranularly formed CuMgZn compound. It was oxidized at 390 °C to 500 °C up to 5 h in air. The oxide scales were thin and compact below 430 °C, but became porous and loose above 450 °C. They consisted primarily of MgO and a small amount of Mg₃N₂. SiC particles were stable over the temperature range explored.     

Corrosion characteristics of Al‐Si‐Mg/SiCp composites with varying Si/Mg molar ratio in neutral chloride solutions

The corrosion resistance of Al‐Mg‐Si/SiC_p composites produced by the pressureless infiltration method [using SiC_p preforms with 50% porosity containing rice hull ash (RHA) and four custom‐made alloys with varying Si/Mg molar ratio] was evaluated in neutral 0.1 M NaCl solutions. The deleterious phase Al₄C₃ was successfully suppressed in composites with Si/Mg molar ratios of 0.89 and 1.05, but not in those with lower Si/Mg molar ratios (0.12 and 0.49). Results of cyclic polarizations in deareated 0.1 M NaCl solutions showed that with increasing Si/Mg molar ratio, passive current density increased but pitting susceptibility decreased both for reinforced and unreinforced alloys. Immersion tests in aerated 0.1 M NaCl showed that for composites with Si/Mg molar ratios of 0.12 and 0.49 chemical degradation by hydrolysis of Al₄C₃ was followed by intense anodic dissolution at the matrix–reinforcement interface, while composites corresponding to Si/Mg molar ratios of 0.89 and 1.05 did not exhibit intense localized attack. Possible reasons for the improvement in resistance to localized corrosion are discussed.     

Formation of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Al Composites by Directed Melt Oxidation of Al-Si-Zn Alloy

Observations are presented on the initiation and growth of Al₂O₃/Al composites by the directed melt oxidation of Al-Si alloys containing metallic Zn or using external dopant ZnO. Thermal gravimetric analysis, optical microscopy, and x-ray diffraction analysis were employed to characterize the progress of oxidation and the nature of oxidation products. Both Zn and ZnO dopants were able to initiate the directed melt oxidation of Al-Si alloys without any Mg being present. Al₂O₃/Al composites were produced when the alloying Zn concentration exceeding 3 wt.%. The incubation period of the oxidation process for Al-Si-Zn alloys was shortened markedly and the amount of composite products increased with the increasing of Zn content in the alloy. In addition, doping with ZnO powder resulted in dense composite formation. A macroscopically planar surface and a fine microstructure promote oxidation growth in Al₂O₃/Al composites. Doping with ZnO powder offers a significant advantage over using metallic Zn for the directed melt oxidation of Al-Si alloy.     

Ti-Si对SiCp/Al基复合材料等离子弧原位焊接性能的影响

以Ti-Si混合粉末作为填充材料,采用氮氩混合等离子气体对SiCp/Al基复合材料进行等离子弧原位焊接,分析SiCp/Al基复合材料的焊接性.结果表明,填充Ti-Si混合粉末进行等离子弧原位焊接时接头组织致密,结合较好,焊缝组织中生成了新的增强颗粒,未发现明显的针状相生成,从而有效地提高了接头的力学性能.力学性能试验表明,采用Ti-Si混合粉末进行等离子弧原位焊接所获得的抗拉强度为232.3MPa.此外探讨了焊接接头中气孔形成的机制以及应采取的相应措施.     

SiCp/Al复合材料与Fe36Ni合金超声波钎焊

利用超声波钎焊方法使用ZnAlSi钎料实现了Fe36Ni合金与45%SiC_p/2024Al和55%SiC_p/A356两种复合材料的连接,并得到由SiC颗粒增强的复合焊缝.通过扫描电镜、能谱等方法对焊缝的微观结构以及断口形貌进行了观察,对接头的压剪强度进行了测试,分析了Fe36Ni与两种复合材料钎焊接头微观组织和接头强度的差异.结果表明,在Fe36Ni与两种复合材料的钎缝中,钎料与两侧母材界面均形成良好的冶金结合,SiC颗粒均匀分布于焊缝中.Fe36Ni与45%SiC_p/2024Al的接头抗剪强度为110~145 MPa,Fe36Ni与55%SiC_p/A356的接头抗剪强度为75~85 MPa.Fe36Ni与45%SiC_p/2024Al的接头断裂位置为钎缝中,而Fe36Ni与55%SiC_p/A356的接头断裂位置位于Fe36Ni与钎料的界面上.