Bonding strength of Al/Mg/Al alloy tri-metallic laminates fabricated by hot rolling

One of major drawbacks of magnesium alloy is its low corrosion resistance, which can be improved by using an aluminized coating. In this paper, 7075 Al/Mg-12Gd-3Y-0·5Zr/7075 Al laminated composites were produced by a hot roll bonding method. The rolling temperature was determined based on the flow stresses of Mg-12Gd-3Y-0·5Zr magnesium alloy and 7075 Al alloy at elevated temperature. The bonding strength of the laminate composites and their mechanism were studied. The effects of the reduction ratio (single pass), the rolling temperature, and the subsequent annealing on the bonding strength were also investigated. It was observed that the bonding strength increased rapidly with the reduction ratio and slightly with the rolling temperature. The bonding strength increases with the annealing time until the annealing time reaches 2 h and then decreases. The mechanical bond plays a major role in the bonding strength.     

Entrance analysis of 7075 Al/Mg–Gd–Y–Zr/7075 Al laminated composite prepared by hot rolling and its mechanical properties

Entrance of 7075 Al/Mg–12Gd–3Y–0.5Zr/7075 Al laminated composites produced by a hot rolling bonding method was investigated. The results showed that using a wedge-end and multi-step process ensured that the assembly of multi-layered plates could enter the rollers area at the beginning of the process. The conventional entrance prerequisite for a single plate during rolling, i.e. having an entrance angle smaller than the friction angle, was not sufficient for multi-layered plates. In addition, a condition for preventing the tail end of the aluminum alloy plates lifting up when these plates come in contact with the rollers must be taken into account. The bonding strength and the ultimate tensile strength of the laminated composite were also studied and it was shown that the mechanical bond played a major role in the bonding strength of the samples produced. The ultimate tensile strength of the laminated composite was lower than that of 7075 Al alloy and higher than that of Mg–12Gd–3Y–0.5Zr Mg alloy. This result could be explained by calculating the stress distribution in the laminated composite under tensile loading.     

Mechanical properties of Cu/SiCp composites fabricated by composite electroforming

The silicon carbide particles (SiC_p) dispersion-strengthened copper matrix composites (Cu/SiC_p) were fabricated by composite electroforming technology. The microstructure, tensile property and wear behavior of Cu/SiC_p composites were investigated. The results showed that composites with different SiC_p contents were obtained. The microstructure of the composite presented a uniform distribution of SiC_p in the matrix and good interfacial integrity. The hardness, yield strength and rigidity of the composites increased with increasing SiC_p content, but at the cost of ductility. Increasing SiC_p content in the composite was not always beneficial to the ultimate tensile strength and wear resistance. The ultimate tensile strength increased with SiC_p content increasing up to 16 vol.% and decreased as exceeding 16 vol.%, and the wear mass loss decreased with SiC_p content increasing up to 21 vol.% and increased again as exceeding 21 vol.%.     

Microstructure and physical properties of Al/diamond composite fabricated by pressureless infiltration

Abstract

The Al/diamond composite was fabricated using a pressureless infiltration method. The microstructure and physical properties of the composite were investigated. The composite has a very low coefficient of thermal expansion (CTE) of 3·9 × 10^?6 K^?1. The thermal conductivity (TC) of the composite is 12% higher than that of the Al alloy matrix. The lower TC of the composite than the expected value was attributed to the existence of interfacial low conducting phases and the porocity of the composite.     

Characterization of hot extruded Mg/SiC nanocomposites fabricated by casting

Mg–1%SiC nanocomposites were fabricated using an ultrasonic cavitation based casting method, resulting in the dispersion of the reinforcing SiC nanoparticles to form Mg–metal matrix nanocomposite (Mg–MMNC) billets. The MMNC billets were then processed using hot extrusion at 350 °C. Micrographic observations illustrate a significant grain size reduction and the presence of microbands that align the SiC nanoparticles parallel to the direction of extrusion for Mg–MMNCs. Observations from the cross-section at 90° of the extrusion direction show uniform nanoparticles dispersion. Results from the extruded Mg–MMNCs tensile testing at different temperatures (25, 125 and 177 °C) reveal an increase of the yield strength, ultimate tensile strength, and ductility values as compared to the un-reinforced and extruded Mg-alloy; such increase was also observed from the microhardness testing results where an increase from 19 to 34% was measured.     

累积叠轧纯Mg/ZK60镁合金层状金属复合材料的组织与性能

采用累积叠轧技术在300℃下制备了纯Mg/ZK60 Mg合金多层复合板材。经过初始复合后,Mg层和ZK60层晶粒明显细化,随着循环次数的增加,Mg/ZK60复合板材两组元晶粒细化并不明显。两种组元的层厚随着循环次数的上升而逐渐降低,两次循环后Mg/ZK60复合板材出现波浪状组织。累积叠轧后,Mg/ZK60复合板材中Mg层和ZK60层呈现典型的轧制织构类型,{0001}基面均向轧制方向发生轻微偏转。Mg/ZK60复合板材的强度及延伸率均介于轧制态的ZK60板与Mg板之间,并随着循环次数的增加逐渐提高。Mg/ZK60复合板材室温阻尼性能和高温阻尼性能均介于纯Mg与ZK60之间,而高温下Mg/ZK60复合板材的高温阻尼则与ZK60板材变化趋势相类似。      

Microstructure and mechanical properties of CP-Ti/X65 bimetallic sheets fabricated by explosive welding and hot rolling

CP-Ti/X65-pipe-steel bimetallic sheet was fabricated by explosive welding and hot rolling (W&R). Trace of the wavy CP-Ti/X65 interface formed from explosive welding was observed along the straight CP-Ti/X65 interface of bimetallic sheet fabricated by W&R. The microstructure and component analysis showed the following. (i) The cross-section of the X65 zone consisted of a 2–5 μm-wide Ti diffusion layer next to the interface, a 150–200 μm-wide decarbonization layer, and the rest area with a banded structure morphology. (ii) There were numerous voids and a slight C element enrichment at the interface. (iii) The section of the CP-Ti zone consisted of a 10–50 μm-wide Fe diffusion zone next to the interface, a residual adiabatic shear band zone next to Fe diffusion zone, and the rest region composed of the α-Ti microstructure. The micro-hardness profile across CP-Ti/X65 interface was measured. The variation patterns of the mechanical properties of the bimetallic sheet in the thickness direction were obtained from stratified tensile tests. The shear test proved that the CP-Ti/X65 bimetallic sheet produced by W&R had acceptable shear bond strength. The microstructure and alloy element distribution across the TA1/X65 interfaces of as-welded, heat treated and extruded TA1/X65 bimetallic sheets were studied and compared.     

粉末增塑挤压制备Al_2O_3/Fe复合型蜂窝材料的组织与性能

为制备性能优良的Al_2O_3/Fe复合型蜂窝材料,首先以316L合金粉末、Al_2O_3粉末和黏结剂为原料,通过粉末增塑挤压及在1 200℃氩气气氛中烧结2h获得了Al_2O_3/Fe复合型蜂窝材料;然后,借助SEM、XRD及万能试验机研究了添加Al_2O_3对Al_2O_3/Fe复合型蜂窝材料组织与性能的影响。结果表明:金属粉末颗粒在烧结过程中结合形成γ-Fe基体网状组织,表面有呈多边形几何状形态的Cr_2O_3形成;添加少量的Al_2O_3可以抑制Cr从基体中析出,降低表面Cr_2O_3的含量,使金属颗粒烧结结合更为紧密,组织表面更加光滑;随着Al_2O_3含量的增加,蜂窝材料表面与催化活性涂层的结合能力增强,复合型蜂窝材料的抗压强度先升高后降低;在Al_2O_3含量为5.0wt%时,抗压强度达26 MPa。所得结论表明5.0wt%Al_2O_3/Fe复合型蜂窝材料力学性能最佳,表面涂覆性能优良。     

Formation of Al3Ti/Mg composite by powder metallurgy of Mg–Al–Ti system

An in situ titanium trialuminide (Al₃Ti)-particle-reinforced magnesium matrix composite has been successfully fabricated by the powder metallurgy of a Mg–Al–Ti system. The reaction processes and formation mechanism for synthesizing the composite were studied by differential scanning calorimetry (DSC), x-ray diffractometry (XRD), scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS). Al₃Ti particles are found to be synthesized in situ in the Mg alloy matrix. During the reaction sintering of the Mg–Al–Ti system, Al₃Ti particles are formed through the reaction of liquid Al with as-dissolved Ti around the Ti particles. The formed intermetallic particles accumulate at the original sites of the Ti particles. As sintering time increases, the accumulated intermetallic particles disperse and reach a relatively homogeneous distribution in the matrix. It is found that the reaction process of the Mg–Al–Ti system is almost the same as that of the Al–Ti system. Mg also acts as a catalytic agent and a diluent in the reactions and shifts the reactions of Al and Ti to lower temperatures. An additional amount of Al is required for eliminating residual Ti and solid-solution strengthening of the Mg matrix.     

Evaluation of microstructure and mechanical properties of Al/Al2O3/SiC hybrid composite fabricated by accumulative roll bonding process

In this investigation, a new kind of metal matrix composites with a matrix of pure aluminum and hybrid reinforcement of Al₂O₃ and SiC particles was fabricated for the first time by anodizing followed by eight cycles accumulative roll bonding (ARB). The resulting microstructures and the corresponding mechanical properties of composites within different stages of ARB process were studied. It was found that with increasing the ARB cycles, alumina layers were fractured, resulting in homogenous distribution of Al₂O₃ particles in the aluminum matrix. Also, the distribution of SiC particles was improved and the porosity between particles and the matrix was decreased. It was observed that the tensile strength of composites improved by increasing the ARB passes, i.e. the tensile strength of the Al/1.6 vol.% Al₂O₃/1 vol.% SiC composite was measured to be about 3.1 times higher than as-received material. In addition, tensile strength of composites decreased by increasing volume fraction of SiC particles to more than 1 vol.%. Scanning electron microscopy (SEM) observation of fractured surfaces showed that the failure mechanism of broken hybrid composite was shear ductile rupture.     

Effect of high temperature annealing and subsequent hot rolling on microstructural evolution at the bond-interface of Al/Mg/Al alloy laminated composites

Using a two-pass hot rolling process, Al(5052)/Mg(AZ31)/Al(5052) alloy laminated composite plates were fabricated. The first pass was performed at relatively low temperatures, and the second pass was performed at higher temperatures. No new phases formed at the bond interface after the first hot rolling pass. High temperature annealing with the annealing temperature at or above 300 °C caused the formation of continuous layers of the intermetallics Mg17Al12 and Al3Mg2 at the bond interface of Al(5052)/Mg(AZ31). The growth rate of the intermetallic layers increased with increasing the annealing temperature, while the incubation time decreased with increasing the temperature. A kinetic equation was developed to describe the growth of the intermetallic compound layers. The second hot rolling pass caused the break of the continuous intermetallic layers into fragments, which were intermittently dispersed at the bond interface.     

Microstructure evolution and mechanical properties in ultrafine grained Al/TiC composite fabricated by accumulative roll bonding

In this study, the influence of nano-TiC particle on microstructure development and mechanical properties of Al/TiC composite fabricated by accumulative roll bonding (ARB) was considered to investigate. Microstructural characterization by electron backscatter diffraction (EBSD) system proved that the grain size decreased to around 200 nm and the TiC reinforcement particles were uniformly distributed in the Al matrix by 7-cycle of the ARB process. It is also found that presence of the TiC particles could accelerate grain refinement. Uniaxial tensile test exhibited that yield and ultimate tensile strength significantly improved more than four times in the 7-cycle ARB processed Al/TiC composite compared with the annealed aluminum specimen which used as the starting material. In addition, the obtained results demonstrated that adding the TiC reinforcement particles could improve the yield strength of the 7-cycle ARB processed Al sheet about 40 percentage.     

Mechanical properties of ultrafine grained ferritic steel sheets fabricated by rolling and annealing of duplex microstructure

A new route to fabricate ultrafine grained (UFG) ferritic steel sheets without severe plastic deformation is proposed in this article. A low-carbon steel sheet with a duplex microstructure composed of ferrite and martensite was cold-rolled to a reduction of 91% in thickness, and then annealed at 620–700 °C. The microstructure obtained through the process with annealing temperatures below 700 °C was the UFG ferrite including fine cementite particles homogenously dispersed. The grain size of ferrite matrix changed from 0.49 to 1.0 μm depending on the annealing temperature. Dynamic tensile properties of the produced UFG steels were investigated. The obtained UFG ferrite–cementite steels without martensite phase showed high strain rate sensitivity in flow stress. The UFG ferritic steels are expected to have high potential to absorb crash energy when applied to automobile body.     

Mechanical properties and damping behavior of woodceramics/ZK60A Mg alloy composite

The mechanical properties and damping behavior of Woodceramics/ZK60A (WCMs/ZK60A, hereafter) composite fabricated by liquid metal infiltration method have been investigated. Experimental results show that ZK60A alloy has infiltrated most of the pores and WCMs/ZK60A composite has an obvious 3-D interpenetrating network structure. Strength and Young’s modulus of the resultant composite are much higher than those of unreinforced woodceramics. Damping values of WCMs/ZK60A composite improve based on those of woodceramics and increase with testing temperature.     

气压烧结Al2O3/TiCN复合材料的力学性能与显微结构

运用二步气压烧结工艺成功制备了Al2O3-30%(质量分数)TiCN复合材料.材料的相对密度达到99.5%,抗折强度为772MPa,硬度为19.6GPa,断裂韧性高达5.82MPa/m2.该材料的烧结过程为固相烧结,烧结过程中TiCN颗粒几乎没有长大,而Al2O3颗粒则长大为原来3倍左右.材料在冷却过程中由于Al2O3和TiCN的热力学性能的失配而引起的界面微应力增长到50MPa左右,不会在材料中导致晶界开裂,但却足以使晶粒发生位错,从而使材料的性能得以增强.     

铸态AZ31镁合金板材等温轧制工艺及组织性能研究

为研究铸态AZ31镁合金轧制工艺及轧制后组织性能,通过试验得到不同道次和变形量对铸态AZ31镁合金板材显微组织和力学性能的影响规律,并采用扫描电子显微镜研究了轧制后板材组织.结果表明,铸态AZ31镁合金板材经等温4道次、等变形量轧制后,板材厚度由20mm变化到4.8 mm,抗拉强度和屈服强度分别达到275 MPa和18...     

Microstructure and mechanical properties of Mg – Al9Zn/SiCp composite produced by vacuum stir casting process

Abstract

15 vol.-% SiC particle reinforced cast Mg – 9AlZn (AZ91C) composite was produced by a vacuum stir casting process, and the microstructure and mechanical properties of the composite investigated. The stirring process was carried out at a speed of 750 – 1500 rev min^-1 with a stainless steel impeller for 25 min in a vacuum of 20 – 40 mbar. SiC particles in the composite exhibited a reasonably homogeneous distribution and were well wetted by magnesium. The Mg – Al9Zn/15SiC_p composite showed significant improvement in yield strength and elastic modulus following T4 heat treatment. The ultimate tensile strength of the composite was low, but close to that of unreinforced magnesium alloy. Mg/SiC interfacial reactions and reaction mechanisms are discussed. No evident interfacial products were found at a low process temperature of 700°C. However, significant chemical reactions at the Mg/SiC interface occurred when the composite melt was maintained at 750°C, and complex reaction products were formed. The fluidity of the composite melt deteriorated seriously after the interfacial reactions occurred.