Microstructure and mechanical properties of AM60B magnesium alloy prepared by cyclic extrusion compression

The cyclic extrusion compression （CEC） process was introduced into the AM60B magnesium alloy. The use of the CEC process was favorable for producing finer microstructures. The results show that the microstructure can be effectively refined with increasing the number of CEC passes. Once a critical minimum grain size was achieved, subsequent passes did not have any noticeable refining effect. As expected, the fine-grained alloy has excellent mechanical properties. The micro-hardness, yield strength, ultimate tensile strength and elongation to failure of two-pass CEC formed alloy are 72.2, 183.7 MPa, 286.3 MPa and 14.0%, but those of as-cast alloy are 62.3, 64 MPa, 201 MPa and 11%, respectively. However, there is not a clear improvement of mechanical properties with further increase in number of CEC passes in AM60B alloy. The micro-hardness, yield strength, ultimate tensile strength and elongation to failure of four-pass CEC formed alloy are 73.5, 196 MPa, 297 MPa and 16%, respectively.

Extrusion force analysis of aluminum pipe fabricated by CASTEX using expansion combination die

To determine the extrusion force of pipe fabricated by continuous casting and extrusion (CASTEX) using an expansion combination die, the metallic expansion combination die was divided into diversion zone, expansion zone, flow dividing zone, welding chamber, and sizing zone, and the corresponding stress formulae in various zones were established using the slab method. The deformation zones of CASTEX groove were divided into liquid and semisolid zone, solid primary gripping zone, and solid gripping zone, and the formulae of pipe extrusion forces were established. Experiments were carried out on the self-designed CASTEX machine to obtain the aluminum pipe and measure its extrusion force using the expansion combination die. The experimental results of radial extrusion force for aluminum pipe are in good agreement with the calculated ones.

Microstructure evolution and mechanical properties of extruded Mg-12Zn-1.5Er alloy

The microstructure and mechanical properties of the cast and extruded Mg-12Zn-1.5Er alloys were investigated. The I-phase observed in the cast Mg-12Zn-1.5Er alloy was broken during hot extrusion. The microstructure of the alloy was refined due to the dynamic recrystallization, and the equiaxed grains have size in the range of 2 5 μm. Moreover, a great deal of nano-scale particles precipitate in the recrystallized grains. Compared with the cast one, the extruded alloy shows a great improvement on the mechanical properties as the result of refined microstructure, the dispersed I-phase and the fine precipitates. The ultimate tensile strength and the yield tensile strength of this extruded alloy are 359 and 318 MPa, respectively.

Low cycle fatigue behavior of T4-treated Al-Zn-Mg-Cu alloys prepared by squeeze casting and gravity die casting

Gravity die casting(GC) and squeeze casting(SC) T4-treated Al-7.0Zn-2.5Mg-2.1Cu alloys were employed to investigate the microstructures,mechanical properties and low cycle fatigue(LCF) behavior.The results show that mechanical properties of SC specimens are significantly better than those of GC specimens due to less cast defects and smaller secondary dendrite arm spacing(SDAS).Excellent fatigue properties are obtained for the SC alloy compared with the GC alloy.GC and SC alloys both exhibit cyclic stabilization at low total strain amplitudes(less than 0.4%) and cyclic hardening at higher total strain amplitudes.The degree of cyclic hardening of SC samples is greater than that of GC samples.Fatigue cracks of GC samples dominantly initiate from shrinkage porosities and are easy to propagate along them,while the crack initiation sites for SC samples are slip bands,eutectic phases and inclusions at or near the free surface.

Microstructure evolution and tensile mechanical properties of thixoformed AZ61 magnesium alloy prepared by squeeze casting

A novel process that combines squeeze casting with partial remelting to obtain AZ61 magnesium alloy with semi-solid microstructures was proposed. In this route, the squeeze casting was used to predeform the magnesium alloy billets to obtain small dendritic structures. During subsequent partial remelting, small dendritic structures transform into globular grains surrounded by liquid films. The results show that the squeeze casting AZ61 alloy after partial remelting produces more ideal, finer semi-solid microstructure compared with as-cast AZ61 alloy treated by the same isothermal holding conditions. Moreover, the mechanical properties of the thixoformed AZ61 alloy prepared by squeeze casting plus partial remelting are better than those of the thixoformed alloy prepared by conventional casting plus partial remelting.

Effect of extrusion process on microstructure and mechanical properties of Ni_3Al-B-Cr alloy during self-propagation high-temperature synthesis

The well-densified Ni3Al-0.5B-5Cr alloy was fabricated by self-propagation high-temperature synthesis and extrusion technique. Microstructure examination shows that the synthesized alloy has fine microstructure and contains Ni3Al, Al2O3, Ni3B and Cr3Ni2 phases. Moreover, the self-propagation high-temperature synthesis and extrusion lead to great deformation and recrystallization in the alloy, which helps to refine the microstructure and weaken the misorientation. In addition, the subsequent extrusion procedure redistributes the Al2O3 particles and eliminates the γ-Ni phase. Compared with the alloy synthesized without extrusion, the Ni3Al-0.5B-5Cr alloy fabricated by self-propagation high-temperature synthesis and extrusion has better room temperature mechanical properties, which should be ascribed to the microstructure evolution.

Microstructures and properties of A356-10%SiC particle composite castings at different solidification pressures

A356-based metal matrix composites with 10% SiC particles of 10 rtm were fabricated by stir casting and direct squeeze casting process under applied pressures of 0.1 （gravity）, 25, 50 and 75 MPa. The microstructures and mechanical properties of the as-cast and T6 heat-treated castings were investigated. The results show that as the applied pressures increase, the casting defects as particle-porosity clusters reduce and the incorporation between the particles and matrix can be improved. The tensile strength, hardness, and coefficients of thermal expansion （CTE） increase with the increase of the pressures. Compared with the as-cast composite castings, the tensile strength and hardness of the heat-treated casting are improved whereas CTEs tend to decrease in T6-treated condition. For the gravity cast composites, there are some particle-porosity clusters on the fracture surface, and the clusters are hardly detected on the fracture surface of the samples solidified at the external pressures. Different fracture behaviors are found between the composites solidified at the gravity and imposed pressures.

Tensile properties and hot extrusion behavior of Zn O-coated Mg_2B_2O_(5w)/6061 Al composites

The 6061 aluminum matrix composites reinforced with ZnO-coated Mg_2B_2O_5w were fabricated by squeeze casting method and followed by extruded under a technical equivalent condition. The mechanical properties and microstructures of the composites were investigated. The results showed that the elastic modulus of the as-cast composites increased straightly with increasing ZnO coating content. The ultimate tensile strength and yield strength of the as-cast composites rapidly increased initially and then declined with increasing ZnO coating content. However, the elongations of all the as-cast composites had similar values. The elongations of the composites were highly enhanced and the ultimate tensile strength of the composite without ZnO coating was the largest after extrusion. A number of whiskers in the composites with ZnO coating were fractured during the extrusion process, but the whiskers＇ breakage extent was limited with the increase of coating content.

车门玻璃与导槽配合偏差对升降影响分析

文章主要研究车门玻璃与导槽安装配合偏差对玻璃升降的影响。考虑玻璃与导槽在Y向的配合偏差,建立玻璃升降轨迹方程和导槽模型,推导出玻璃在升降过程中,玻璃中线距导槽中线的Y向偏移量,进而得到玻璃受到的导槽密封条挤压力公式及升降摩擦力。并在此基础上,以某车型为例子,计算玻璃与导槽出现Y向配合偏差后,玻璃在上升过程中,玻璃受到的导槽密封条的挤压力以及摩擦阻力,并分析对玻璃升降的影响。

Effects of second phases on mechanical properties and martensitic transformations of ECAPed TiNi and Ti-Mo based shape memory alloys

TiNi and Ti-based shape memory alloys were processed by equal channel angular pressing （ECAP） at 673-773 K along Bc route to obtain ultrafine grains for increasing the strength of parent phase and improving the functional properties. The effects of both thermodynamically stable and metastable second phases on the mechanical properties and martensitic transformations of these alloys were investigated. It is found that thermodynamically stable Ti2Ni phase has no effect on martensitic transformation and superelasticity of Ti-rich TiNi alloy, thermodynamically stable α phase is harmful for ductility of Ti-Mo-Nb-V-Al alloy, but metastable Ti3Ni4 phase is effective for R phase transformation, martensitic transformation and superelasticity of Ni-rich TiNi alloy. The mechanisms of the second phases on the martensitic transformations and mechanical properties were discussed.

Effects of Gd on microstructure and mechanical property of ZK60 magnesium alloy

Microstructures and phase compositions of as-cast and extruded ZK60-xGd （x=0-4） alloys were investigated. Meanwhile, the tensile mechanical property was tested. With increasing the Gd content, as-cast microstructure is refined gradually. Mg-Zn-Gd new phase increases gradually, while MgZn2 phase decreases gradually to disappear. The second phase tends to distribute along grain boundary by continuous network. As-cast tensile mechanical property is reduced slightly at ambient temperature when the Gd content does not exceed 2.98%. After extrusion by extrusion ratio of 40 and extrusion temperature of 593 K, microstructure is refined further with decreasing the average grain size to 2 μm for ZK60-2.98Gd alloy. Broken second phase distributes along the extrusion direction by zonal shape. Extruded tensile mechanical property is enhanced significantly. Tensile strength values at 298 and 473 K increase gradually from 355 and 120 MPa for ZK60 alloy to 380 and 164 MPa for ZK60-2.98Gd alloy, respectively. Extruded tensile fractures exhibit a typical character of ductile fracture.

Effects of extrusion and heat treatments on microstructure and mechanical properties of Mg-8Zn-1Al-0.5Cu-0.5Mn alloy

The effects of extrusion and heat treatments on the microstructure and mechanical properties of Mg-8Zn-1Al-0.5Cu- 0.5Mn magnesium alloy were investigated. Bimodal microstructure is formed in this alloy when it is extruded at 230 and 260 ℃, and complete DRX occurs at the extruding temperature of 290 ℃. The basal texture of as-extruded alloys is reduced gradually with increasing extrusion temperature due to the larger volume fraction of reerystallized structure at higher temperatures. For the alloy extruded at 290 ℃, four different heat treatments routes were investigated. After solution ＋ aging treatments, the grains sizes become larger. Finer and far more densely dispersed precipitates are found in the alloy with solution ＋ double-aging treatments compared with alloy with solution ＋ single-aging treatment. Tensile properties are enhanced remarkably by solution ＋ double-aging treatment with the yield strength, tensile strength and elongation being 298 MPa, 348 MPa and 18%, respectively. This is attributed to the combined effects of fine dynamically reerystallized grains and the uniformly distributed finer precipitates.

Grain refinement and mechanical properties of pure aluminum processed by accumulative extrusion bonding

Ultrafine-grained aluminum processed by a new severe plastic deformation technique, accumulative extrusion bonding (AEB), was investigated. Microstructural characterization indicated good interfacial bonding and an average grain size of ~440 nm was obtained after six passes. Tensile testing revealed that the strength reached the maximum value of 195 MPa and the total elongation exceeded 16% after five passes. The hardness was also significantly improved and almost reached saturation after the first pass. SEM fractography of AEB-processed specimens after tensile test showed that failure mode was shear ductile fracture with elongated shallow dimples. Comparison with conventional accumulative roll bonding indicates that this new AEB technique is more effective in refining grain and improving mechanical properties of the specimens.

Simultaneous improvement in strength and ductility of extruded Mg alloy via novel closed forging extrusion

A novel continuous plastic process employed on AZ31 Mg alloy called closed forging extrusion(CFE)was presented.The optical microscopy,scanning electron microscopy,electron back-scatter diffraction and tensile and compressive tests were employed to investigate the microstructure evolution and strengthening mechanism.The results indicated that the CFE-process can promote dynamic recrystallization(DRX),eliminate the coarsen unDRXed grain regions,refine the grains effectively,and improve the strength,plasticity and anisotropy of the alloy.The grain refinement was mainly attributed to the stress,which facilitated the nucleation of recrystallization and refined the microstructure via the CFE.The fully DRXed ultrafine grained structure improved the strength and plasticity simultaneously.After 60 s closed forging and continuous extrusion,the alloy exhibits relatively high TYS,UTS,CYS,elongation and yield asymmetry of 305 MPa,337 MPa,295 MPa,27%and 0.97,respectively.

Effect of extrusion ratio on microstructure and mechanical properties of AZ91D magnesium alloy recycled from scraps by hot extrusion

A method for recycling AZ91D magnesium alloy scraps directly by hot extrusion was studied.Various microstructural analyses were performed using the techniques of optical microscopy,scanning electron microscopy(SEM)and energy dispersive spectroscopy(EDS).Microstructural observations revealed that all the recycled specimens consisted of fine grains due to the dynamic recrystallization.The main strengthening mechanism of the recycled specimen was grain refinement strengthening and homogeneous distribution of oxide precipitates.The interfaces of individual scraps of extruded materials were not identified when the scraps were extruded with the extrusion ratio of 40-1.Oxidation layers of the scraps were broken into pieces by high compressive and shear forces under the extrusion ratio of 40-1.The ultimate tensile strength and elongation to failure increased with increasing the extrusion ratio.Recycled specimens with the extrusion ratio of 40:1 showed higher ultimate tensile strength of 342.61 MPa and higher elongation to failure of 11.32%,compared with those of the cast specimen.

Microstructure and mechanical properties of as-cast and extruded Mg–8Li–3Al–0.7Si alloy

Mg–8Li–3Al–0.7Si alloy was prepared by casting and deformed by hot extrusion in this study.And the microstructure of as-cast and extruded specimens was analyzed with OM,XRD,SEM and EDS.Results show that the specimens are composed ofα-Mg,β-Li,AlLi,MgLiAl2 and Mg2Si phases.In as-extruded specimen,the microstructure is refined and theβ-Li phase has the effect of coordination during deformation.After hot extrusion,Chinese script Mg2Si phase is crushed into block-like and distributes uniformly in the matrix.Mechanical properties results show that the strength and elongation are both improved after hot extrusion.

Effects of Sr addition on microstructure, mechanical properties and in vitro degradation behavior of as-extruded Zn-Sr binary alloys

The microstructures,mechanical properties and in vitro degradation behavior of as-extruded pure Zn and Zn-x Sr(x=0.1,0.4,0.8 wt.%)alloys were investigated systematically.For the microstructure and mechanical properties,Sr Zn13 phase was newly formed due to the addition of 0.1 wt.%Sr,improving the yield strength,ultimate tensile strength and elongation from(85.33±2.86)MPa,(106.00±1.41)MPa and(15.37±0.57)%for pure Zn to(107.67±2.05)MPa,(115.67±2.52)MPa and(20.80±2.19)%for Zn-0.1Sr,respectively.However,further increase of Sr content led to the deterioration of the mechanical properties due to the stress concentration and cracks initiation caused by the coarsening Sr Zn13 particles during tensile tests.For in vitro degradation,since micro galvanic corrosion was enhanced owing to the formation of the inhomogeneously distributed Sr Zn13 phase,the corrosion mode became non-uniform.Corrosion rate is gradually increased with the addition of Sr,which is increased from(11.45±2.02)μm/a(a=year)for pure Zn to(32.59±3.40)μm/a for Zn-0.8Sr.To sum up,the as-extruded Zn-0.1Sr alloy exhibited the best combination of mechanical properties and degradation behavior.

Production of AZ80/Al composite rods employing non-equal channel lateral extrusion

In order to simultaneously take the advantages of magnesium and aluminum alloys, AZ80/A1 composite rods were produced using non-equal channel lateral extrusion （NECLE） process at different temperatures. Scanning electron microscope （SEM） and energy dispersive spectrometer （EDS） tests as well as the shear punch test were employed to study the quality and strength of the bond between the two alloys. It was found that the process temperature was an important factor affecting the level of interfacial bonding, such that increasing the temperature from 250 to 300℃ has improved the strength by 37% and the thickness of the bond between the layers by 4.5%. Moreover, this temperature rise reduced the maximum required forming load by 13%. However, the hardness tests showed that this increase in the process temperature resulted in 4% decrease in the hardness of the composite bar.

Properties inhomogeneity of AM60 magnesium alloy processed by cyclic extrusion compression angular pressing followed by extrusion

A new severe plastic deformation(SPD)technique for improvement of the metallurgical properties of the magnesium alloys is presented.In this process,a cyclic extrusion compression angular pressing(CECAP)process is followed by an extrusion step in the outlet playing the role of additional back pressure.Therefore,more uniform and enhanced mechanical properties are expected in comparison with equal channel angular pressing(ECAP).In order to evaluate the effectiveness and capabilities of this new method,an AM60 magnesium alloy was processed.Finite element results exhibited a significant increase in strain values as well as uniform strain distribution for the new method.In addition,~110%increase in compressive stress was observed in new method compared to the conventional ECAP.Experimental results revealed a noticeable increase in the hardness and strength of the specimens processed by the new technique as a result of the formation of finer grains and more homogeneous microstructure with good distribution of refinedβ-phase along the boundaries.It may be concluded that the new process is very promising for future magnesium alloy products.

Novel method of screw extrusion for fabricating Al/Mg(macro-) composites from aluminum alloy 6063 and magnesium granules

A novel method of screw extrusion was used for producing a bimetal composite Al/Mg from granules containing aluminium alloy 6063 （AA6063） and commercial pure magnesium. Up to 12.5%（mass fraction） pure magnesium was added to the aluminium alloy. In general, the material consisted of a fine grained microstructure. In addition to the phases originating from the input materials, intermetallic phases were observed as islands consisting of the Al2Mg3 phase surrounded byγ-Mg17Al12, throughout the microstructure. The mechanical properties of the extruded material showed a gradual increase in strength with increasing the addition of Mg. The highest registered UTS, well above 350 MPa, was observed for the material containing 10%Mg. Examinations of the fracture surfaces indicated that increasing the magnesium content led to a higher degree of brittle fracture and a gradual change of the fracture micro-mechanisms. The optimization of the post-extrusion processing conditions is still ongoing.