Hardness, Wear Resistance and nacture Toughness of Cast Hiduminium/Corundum Particulate Composites

This paper reports some results obtained in an investigation to see how increasing the corundum dispersoid content from 0% to 7% in a matrix of as-cast and wrought hiduminium alloy affects the hardness. wear resistance and fracture toughness of the composite. The results show that as the corundum content is increased, the hardness and the wear resistance increase remarkably,whereas the fracture toughness drops significantly. It was found that Just a minute amount of corundum is sufficient to cause a fairly large change in these mechanical properties. The hardness of the material is also affected signifIcantly by the aging time. Moreover, if other factors are kept constant, hot extrusion improves both its hardness and its wear resistance. whereas the fracture toughness is decreased     

搅拌铸造SiCp/2024复合材料热挤压-轧制变形组织及性能

利用搅拌铸造-热挤压-轧制工艺制备SiCp/2024复合材料薄板。通过金相观察(OM)、扫描电镜(SEM)及力学测试等手段研究了该复合材料在铸态、热挤压态及轧制态下的显微组织及力学性能,分析了材料在塑性变形过程中显微组织及力学性能的演变。结果表明,该复合材料铸坯主要由80～100μm的等轴晶组成,粗大的晶界第二相呈非连续状分布,SiC颗粒较均匀地分布于合金基体中;热挤压变形后,晶粒沿挤压方向被拉长,SiC颗粒及破碎的第二相呈流线分布特征;轧制变形后,基体合金组织进一步细化,晶粒尺寸为30～40μm,SiC颗粒破碎明显,颗粒分布趋于均匀,轧制变形对挤压过程中形成的SiC颗粒层带状不均匀组织有显著的改善作用。数学概率统计指出,塑性变形有利于提高颗粒分布的均匀性。力学测试表明,塑性变形后,复合材料的抗拉强度、屈服强度和延伸率显著提高。SiCp/2024铝基复合材料主要的断裂方式为:合金基体的延性断裂、SiC颗粒断裂及SiC/Al界面脱粘。     

Damage of 6061/SiCw composite by thermal cycling

The unreinforced 6061 alloy and a 6061/SiC composite, at the beginning of the T6 temper, were submitted to thermal cycling (up to 2000 cycles) in the temperature ranges 25–180 °C and 25–220°C. The microstructure of these materials was studied by scanning electron microscopy and mercury intrusion porosimetry. Mechanical and thermomechanical properties were also investigated. Tensile strength, hardness, Charpy impact resistance, fracture toughness, density, specimen dimensions and thermal expansion were compared before and after thermal cycling. The unreinforced alloy showed an increase of ductility with cycling. This behaviour was chiefly due to overageing and partial annealing. The composite material, following the thermal treatment, did not only undergo overageing and annealing of its metal matrix; void coalescence, crack formation and reinforcement debonding were also observed. The development of these defects basically resulted in a marked decrease of tensile strength, yield strength, Charpy impact energy and fracture toughness. This revised version was published online in November 2006 with corrections to the Cover Date.     

Tensile properties and fracture behavior of partial squeeze added slow shot die-cast A356 aluminum alloy

In this contribution, effect of the microstructural characteristics on tensile properties and fracture behavior of partial squeeze added slow shot die-cast A356 alloy die casting in the as-cast and T6 heat-treated conditions was studied. The results show that, inferior tensile properties of the casting partial squeeze part were caused by the heterogeneity of α-Al cells with fragment, rosette, angular and globular shapes, while finer dendrites with smaller secondary dendrite arm spacing and more rounded silicon particles corresponded to higher tensile properties. After T6 treatment, tensile properties increased significantly, due to the spheroidization of silicon particle and consequently the reduction of stress concentration at silicon/eutectic matrix interface. Differences observed in the tensile fracture path were attributed to microstructural changes as well as morphological aspects of silicon phase.     

Effect of thermal treatment on the mechanical and toughness properties of extruded SiCw/aluminium 6061 metal matrix composite

Mechanical, instrumented Charpy V-notch (CVN) energy and plane strain fracture toughness properties of SiC whisker reinforced-6061 aluminium metal matrix composite material from an extruded tube have been determined. The effect of thermal treatment and orientation have been studied. The mechanical strength properties are higher than wrought Al 6061 in the T6 condition. CVN energy values, however, were reduced by an order of magnitude.K _lc fracture toughness of the as-received, T6 and degassed + T6 thermal treatments were 50% of the wrought Al 6061 alloy. The effect of orientation showed that the orientation with the least amount of SiC whisker in the crack plane (i.e. greatest mean free path between reinforcements) yields the highest toughness value.     

Hot Extrusion Process Effect on Mechanical Behavior of Stir Cast Al Based Composites Reinforced with Mechanically Milled B4C Nanoparticles

In this study, aluminum alloy (Al-2 wt% Cu) matrix composites reinforced with 1, 2 and 4 wt% boron carbide nanoparticles fabricated through mechanical milling with average size of 100 nm were fabricated via stir casting method at 850℃. Cast ingots of the matrix alloy and the composites were extruded at 500℃ at an extrusion ratio of 10:1 to investigate the effects of hot extrusion on the mechanical properties of the composites. The microstructures of the as-cast and the extruded composites were investigated by scanning electron microscopy (SEM). Density measurement, hardness and tensile tests were carried out to identify the mechanical properties of the composites. The extruded samples revealed a more uniform distribution of B4C nanoparticles. Also, the extruded samples had strength and ductility values superior to those of the as-cast counterparts. In the as-cast and the extruded samples, with increasing amount of B4C nanoparticles, yield strength and tensile strength increased but elongation to fracture decreased.     

Forging of the AA2618/20 vol.% Al2O3p composite: Effects on microstructure and tensile properties

The use of aluminium-based particulate reinforced MMCs for automotive components and aircraft structures have been shown to be highly advantageous over their unreinforced alloys, due to their high specific strength and stiffness and superior wear resistance in a wide temperature range. The aim of this paper was to evaluate the effect of the hot forging process on the microstructure and tensile properties (at room and high temperature) of a MMC based on the aluminium alloys AA2618 reinforced with 20 vol.% of alumina particles (Al₂O_3p). Microstructural analyses of the as-cast and heat-treated composite showed large grain size of the aluminium alloy matrix and a quite non-homogeneous distribution of the reinforcing particles. The forging process led to an evident grain refinement, while it did not lead to significant variations in the size and distribution of the reinforcement particles. Regarding the effect of the forging process on the mechanical properties, it induced a slight increase in hardness, tensile strength, elastic modulus and an evident increase in tensile elongation. SEM analyses of the fracture surfaces of the tensile specimens showed substantially similar morphologies for the as-cast and forged composites, both at room and high temperature. The mechanism of damage was mainly decohesion at the matrix–particle interface.     

Development of mechanical properties in AA 8090 alloy produced by extrusion processing

Abstract

The effects of extrusion processing parameters on the mechanical properties of an AA 8090 alloy were monitored using a combination of hardness, tensile, andfracture toughness tests, and using light, transmission electron microscopy, and scanning electron microscopy. It was found that variations in the processing parameters affect the tensile properties to a greater extent in the as extruded condition than in the heat treated condition. In the former, the property changes occur as a result of both variation of grain structure and the solutionising effect during the process. In the latter, the tensile properties are controlled by the precipitation processes that occur, and the toughness remains essentially unaffected by changes in the processing conditions. Improved combinations of strength, ductility, and toughness are achieved when the material is subjected to suitable preaging treatments, which modify the precipitate morphology within the microstructure; the fracture surface characteristics of both tensile and fracture toughness test specimens reflect the microstructural changes.

MST/1115     

铸态Mg-4Al-2Si合金的显微组织与力学性能

采用重力铸造法制备Mg-4Al-2Si(AS42)镁合金,研究了铸态合金的显微组织和室温力学性能。结果表明:铸态AS42合金主要由α-Mg基体、β-Mg17Al12相及Mg2Si相组成;β-Mg17Al12相呈网状和棒状分布于晶界上,粗大的汉字状Mg2Si相沿晶界或穿晶分布,多边形块状Mg2Si相随机分布于基体组织中。铸态合金的硬度为64.5 HV,室温抗拉强度为113.5 MPa,屈服强度为86 MPa,伸长率为4.1%;拉伸断裂形式为准解理脆性断裂。     

Microstructure and mechanical properties of a sand-cast Mg–Nd–Zn alloy

The microstructures and mechanical properties of a sand-cast Mg–Nd–Zn alloy in the as-cast, solution-treated and peak-aged conditions were investigated. The as-cast alloy was comprised of α magnesium matrix and Mg₁₂Nd eutectic compounds. The eutectic compounds dissolved into the matrix and small Zr-containing particles precipitated at grain interiors, due to the solution treatment. After the solution treatment, two kinds of cooling manner, either cooling in air or quenching in water, were employed. It was worth noting that some basal precipitates formed in the matrix during the in-air cooling process after solution treatment, which led to the succedent weak ageing hardening response and low strength in peak-aged condition. The hardness, yield strength, ultimate tensile strength and elongation at room temperature, of the samples in the T61 condition, were HV81, 191 MPa, 258 MPa and 4.2%, respectively. When tensile tested at high temperature, they exhibited serrated flow. Moreover, the casting surface of the tensile testing bar also had a great influence on its mechanical properties.     

Effect of microstructure on the mechanical properties and fracture of commercial hypoeutectic Al-Si alloy modified with Na, Sb and Sr

The microstructure, hardness, tensile properties and fracture have been studied for the non-modified and modified aluminium (Al) silicon (Si) commercial hypoeutectic alloy. Three modifiers were used being sodium (Na), antimony (Sb) and strontium (Sr). The Sb-modified structure revealed small plate-like Si morphology. The Na and Sr-modified structures exhibited fibrous Si. A slight increase in the hardness values (HV) due to modification was observed. A general increase in the tensile properties was observed due to modification. The tensile properties of the sand mould Sr-modified alloy were significantly higher than those of the Na-modified alloy by 12.7% in proof stress, 16.3% in ductility and 33.3% in toughness. For the metal mould ingots the increase in tensile properties of Sr-modified alloy were respectively: 16.7%, 32.5% and 41.7% compared to a Na-modified alloy. Optical fractography on longitudinal sections near the fracture surfaces of the modified alloys revealed that the crack propagates in the eutectic thus, circumventing the Al-dendrites. The dimple and smooth ripple patterns observed by scanning electron microscope (SEM) on the fracture surface of the Na and Sr-modified alloys suggest a transgranular type of fracture across the grains of the eutectic matrix.     

Evaluation of mechanical properties of aluminium alloy–alumina–boron carbide metal matrix composites

This paper deals with the fabrication and mechanical investigation of aluminium alloy, alumina (Al₂O₃) and boron carbide metal matrix composites. Aluminium is the matrix metal having properties like light weight, high strength and ease of machinability. Alumina which has better wear resistance, high strength, hardness and boron carbide which has excellent hardness and fracture toughness are added as reinforcements. Here, the fabrication is done by stir casting which involves mixing the required quantities of additives into stirred molten aluminium. After solidification, the samples are prepared and tested to find the various mechanical properties like tensile, flexural, impact and hardness. The internal structure of the composite is observed using Scanning Electron Microscope (SEM).     

Studies on the development of aluminium alloy–mild steel reinforced composite

With a view to developing a new metal–metal cast composite material as a possible substitute for ferrous materials in wear resistant applications, Al alloy (LM11) is reinforced with mild steel (ms) wires and it is heat treated to get ‘reaction interface’ (RI). Microhardness, tensile properties and wear characteristics of the matrix, as-cast and heat treated composites have been determined. While microhardness of the composite showed variation from 150 to 45 VHN across the interface in the as-cast composite, annealed (500–525°C) composite showed a microhardness of 350–420 VHN at the interface indicating the effectiveness of the heat treatment. It is seen that the % improvement in wear resistance increased with increase in number of wires when embedded in the aluminium alloy matrix. Further imrpovement of about 30% was observed when heat treated at 500°C for 15 h. These results have been discussed in terms of wetting between ms wires and the matrix, particularly the increase of hardness and tensile strength to the formation of ‘reaction interface’ due to annealing. The width of the interface increased with annealing time and temperature and the kinetics of reaction followed logarithmic and parabolic growth rate. The activation energy for the formation of intermetallics constituting the reaction interface is found to be 20.7 KJ mol⁻¹. From the measured hardness and ultimate tensile strength of the constituents and composites an empirical relation was deduced.     

Microstructure and mechanical properties of Hadfield steel matrix composite reinforced with oriented high-chromium cast iron bars

To obtain a compatible material of high hardness and high toughness, Hadfield steel matrix was reinforced by oriented high-chromium cast iron bars. The mechanical behaviors of the as-cast and water-quenched composites were comparatively studied with a Hadfield steel substrate. The experimental results showed that the alloy powders inside the flux-cored welding wires could be melted by the heat capacity of Hadfield steel melt and became high-chromium cast iron bars. The impact toughness of the water-quenched composite was higher than that of the as-cast composite and lower than that of the Hadfield steel. The wear rate of the water-quenched composite was 1.23 mg/h m² at 0.3 kg and 2.93 mg/h m² at 1.2 kg, which was lower compared with those of the as-cast composite and Hadfield steel. The impact toughness and wear resistance of the water-quenched composite were related not only to the combining actions of the Hadfield steel matrix and high-chromium cast iron bars but also to the effect of heat treatment. The wear behavior of the water-quenched composite was industrially tested as pulverizer plate.     

铸态Mg-4Al-4Si-0.75Sb合金的显微组织与力学性能

采用重力铸造法制备Mg-4Al-4Si-0.75Sb(AS44-0.75Sb)(质量分数/%,下同)镁合金,研究铸态合金的显微组织和室温力学性能。结果表明:铸态AS44-0.75Sb合金主要由α-Mg基体、β-Mg17Al12相、Mg2Si相和Mg3Sb2相组成;加入0.75Sb后形成高熔点的Mg3Sb2相,显著改善了Mg2Si相的形貌,使粗大的骨骼状Mg2Si转变为相对细小的汉字状Mg2Si。铸态合金的硬度HV为65.9,屈服强度为136.4MPa,抗拉强度为172.3MPa,伸长率为3.3%;拉伸断裂形式为准解理脆性断裂。     

Fracture toughness of recycled AISI 1040 steel chip reinforced AlMg1SiCu aluminum chip composites

In this paper, a method of recycling aluminum and steel chip is presented by applying powder methodology. This method consists of the composite production, cold pressing, a new sintering method, definition of mechanical properties and fracture toughness. AISI 1040 steel chip was used as reinforcement materials and AlMg1SiCu aluminum chip were used as matrix materials. AISI 1040 steel chip reinforcement was added into the matrix for 20%, 30% and 40% weight ratios. To determine the mechanical behaviors of composites, compressive strength, three point bending, hardness and fracture toughness, initial notch depth method tests were performed at ambient condition. It was observed that steel chip reinforcement provided increased compressive strength and hardness, but the fracture toughness of composites decreased versus to increasing steel content. Considering analyses of microscopic micrographs of composites (SEM), by increasing steel content causes an increase in the angular facets on fracture surfaces.     

Mechanical properties of SG-iron with different matrix structure

Spheroidal graphite (SG) irons with a variety of matrix-structure have been produced. The correlation between tensile properties, impact toughness, hardness and pearlite content is investigated. The pearlite content is varied from 0 to about 95 per cent by the use of different heat treatment processes. The apparent variation in the properties with the pearlite level reveals the remarkable consistency in the relationships between mechanical properties and pearlite content. The study of the tensile properties showed that the yield and ultimate tensile strengths are increased with increasing pearlite level in the matrix structure. For matrix structure with 94.6% pearlite, the increases are about 91% and 98%, respectively, compared with those of the ferritic matrix material. The impact toughness of SG-iron is influenced significantly by matrix microstructure. Energy of about 230 × 10³J/m² is required to fracture a ferritic matrix SG-iron. On the other hand, when the matrix structure approaches a fully pearlitic matrix the fracture energy is decreased by an amount of 75.5%. The Brinell hardness value is found to increase with increasing pearlite content in the matrix structure of the present material. It increases from about 128 for a fully ferritic matrix to about 258 as the matrix structure approaches a fully pearlitic condition. This change in the hardness value reflects the change in the mechanical properties presented in this study.     

SiCw＋B4Cp／MB15镁基复合材料力学性能与微观结构

对真空反压浸渍方法制备的挤压态ＳｉＣＷ＋Ｂ４ＣＰ／ＭＢ１５镁基复合材料及基体合金进行了一系列的力学性能测试，并用ＳＥＭ观察增强剂分布与断口形貌，用ＴＥＭ和ＥＤＳ方法对复合材料的界面结构进行分析。研究结果表明，上述复合材料同基体相比有更高的强度、弹性模量和比强度、比弹性模量。深浸蚀ＳＥＭ相分析表明均匀排布的晶须、颗粒起到很好的增强效果。复合材料的断口有晶须露头与韧窝存在，该复合材料具有一定的韧性；并在ＳｉＣ／ＭＢ１５界面上发现Ｚｎ析出相。     

双屏蔽(B4C-W)/6061Al层状复合板设计与性能

基于B₄C和W良好的屏蔽中子和γ射线性能,采用6061铝合金作为基体,设计了一种新型双屏蔽(B₄C-W)/6061Al层状复合材料,通过放电等离子烧结后加热轧制成板材,对制备的复合材料微观组织和力学性能进行了研究。结果表明,屏蔽组元B₄C和W颗粒均匀地分布在6061Al基体中,层界面、B₄C/Al、W/Al异质界面之间结合良好,无空隙和裂纹。在颗粒与基体界面处形成扩散层,扩散层的厚度约为6 μm (W/Al)和4 μm (W/Al)。轧制态的(B₄C-W)/6061Al层状复合板的屈服强度(109 MPa)和极限抗拉强度(245 MPa)明显优于烧结态的复合材料,但断裂韧性降低。强度提高的原因主要是轧制后颗粒的二次分布、均匀性及界面结合强度提高,基体合金的晶粒尺寸减小,位错密度增加。层状复合板的断裂方式为基体合金的韧性断裂和颗粒的脆性断裂。