Microstructure and mechanical properties of Mg -2Gd -3Y -0.6Zr alloy upon conventional and hydrostatic extrusion

The Mg-12Gd-3Y-0.6Zr (wt. %) alloy was subjected to conventional and hydrostatic extrusion in two subsequent steps. The best combination of mechanical properties (strength and ductility) was achieved by RT hydrostatic extrusion following conventional extrusion at 430 °C, with the ultimate tensile strength (UTS), tensile yield strength (TYS) and elongation being 485 MPa, 413 MPa and 5.2% at room temperature. The texture results of extruded rods indicate that the c-axis of most grains was aligned preferentially perpendicular to the extrusion direction, forming a typical extrusion Mg fiber texture.     

Microstructures and mechanical responses of powder metallurgy non-combustive magnesium extruded alloy by rapid solidification process in mass production

Spinning Water Atomization Process (SWAP), which was one of the rapid solidification processes, promised to produce coarse non-combustible magnesium alloy powder with 1–4 mm length, having fine α-Mg grains and Al₂Ca intermetallic compounds. It had economical and safe benefits in producing coarse Mg alloy powders with very fine microstructures in the mass production process due to its extreme high solidification rate compared to the conventional atomization process. AMX602 (Mg–6%Al–0.5%Mn–2%Ca) powders were compacted at room temperature. Their green compacts with a relative density of about 85% were heated at 573–673 K for 300 s in Ar gas atmosphere, and immediately consolidated by hot extrusion. Microstructure observation and evaluation of mechanical properties of the extruded AMX602 alloys were carried out. The uniform and fine microstructures with grains less than 0.45–0.8 μm via dynamic recrystallization during hot extrusion were observed, and were much small compared to the extruded AMX602 alloy fabricated by using cast ingot. The extremely fine intermetallic compounds 200–500 nm diameter were uniformly distributed in the matrix of powder metallurgy (P/M) extruded alloys. These microstructures caused excellent mechanical properties of the wrought alloys. For example, in the case of AMX602 alloys extruded at 573 K, the tensile strength (TS) of 447 MPa, yield stress (YS) of 425 MPa and 9.6% elongation were obtained.     

Design of powder metallurgy aluminium alloys for applications at elevated temperatures Part 2 Tensile properties of extruded and Conformed gas atomised powders

Abstract

The effects of aging treatments on the tensile properties and microstructure of Al–Cr–Zr–Mn powder metallurgy aluminium alloys prepared from high pressure gas atomised powders were investigated. The alloy compositions were designed to give powders with or without Al₁₃Cr₂ intermetallics in the <45 μm size fraction. The Al–5·2Cr–1·4Zr–1·3Mn alloy is typical of the former (concentrated alloy) and the Al–3·3Cr–0·7Zr–0·7Mn alloy of the latter (dilute alloy). The alloys were prepared using a canning/degassing/extrusion sequence or the Conform consolidation process. Measurements of micro hardness and electron microscopy were used to correlate the microstructure with the tensile properties. The extruded powders of both alloys exhibited better properties than those of the Conformed powders. A large contribution to the strength of the extruded materials is made by their stabilised fine grain size. The dilute alloys had consistently better ductility. Neither alloy retained its strength after prolonged aging at 400°C, but the results indicate that a service temperature of 300°C may be possible.

MST/1247b     

The microstructure,tensile, and shear deformation behavior of an AZ31 magnesium alloy after extrusion and equal channel angular pressing

The shear punch testing (SPT) technique and the uniaxial tension tests were employed to evaluate the mechanical properties of the equal channel angularly pressed (ECAPed) AZ31 magnesium alloy. After extruding, the material was ECAPed for 1, 2, and 4 passes using route B_C. The grain structure of the material was refined from 20.2 to 1.6 μm after 4 passes of ECAP at 200 °C. The 4 pass ECAPed alloy showed lower yield stress and higher ductility as compared to the as-extruded condition, indicating that texture softening has overcome the strengthening effects of grain refinement. The same trends in strength and ductility were also observed in shear punch testing. Similar shear strength and ductility values of the samples taken perpendicular to the extrusion direction (ED) and normal direction (ND) after 4 passes of ECAP indicated that {0 0 0 2} basal planes were inclined (∼45°) to the extrusion axis. The shear punch testing technique was found to be a useful method for verifying directional mechanical properties of the miniature samples of the ECAPed magnesium alloys.     

挤压温度对Mg-5.3Gd-2.6Y-1.1Nd-0.3Zr合金的力学性能和耐生物腐蚀性能的影响

在不同温度下对均匀化处理后的Mg-5.3Gd-2.6Y-1.1Nd-0.3Zr(质量分数/%)镁合金进行挤压。利用光学显微镜和拉伸实验对比研究固溶态铸锭、不同挤压温度合金的显微组织和力学性能,采用析氢法、失重法和极化曲线实验综合测试合金在Hank’s人体模拟液中的耐生物腐蚀性能,利用扫描电子显微镜观察腐蚀后合金的表面腐蚀形貌。结果表明:随着挤压温度的降低,合金的晶粒不断细化,强度及塑性不断提高,其中390℃温度下挤压得到的合金屈服强度达到223.4MPa,较固溶态铸锭(139.8MPa)提升约60%,且挤压后的合金在Hank’s体液中具有更高的耐腐蚀性,随着挤压温度的降低,合金的耐蚀性先升高后降低,450℃挤压的棒材耐生物腐蚀性能最优,腐蚀速率为0.74mm/a。     

Formability,mechanical and corrosive properties of Mg–Nd–Zn–Zr magnesium alloy seamless tubes

Some large Mg–3.0Nd–0.2Zn–0.4Zr (NZ30K) magnesium alloy seamless tubes were prepared by forward extrusion. The as-extruded tubes were cooled in the air or by spraying liquid N₂ after extrusion. The formability, mechanical and corrosive properties of the NZ30K magnesium alloy seamless tubes were investigated. The experimental results show that seamless NZ30K tubes with an outer diameter of 110 mm and inner diameter of 90 mm can be produced by forward extrusion and the tubes have good roundness, concentricity and straightness even without any straightening. The tensile results show that the maximum ultimate tensile strength, yield strength and elongation of the extruded tubes cooled in the air and by spraying liquid N₂ are 306.3 and 314.6 MPa, 250.4 and 270.3 MPa, 14.2% and 15.6%, respectively. The corrosion rates of the as-extruded tubes cooled in the air and by spraying liquid N₂ immersed in 5% NaCl solution for 3 days are 0.225 and 0.234 mg cm⁻² day⁻¹, respectively, which are a little inferior to the as-cast, T4 and T6 NZ30K alloys, but much lower than that of AZ91 alloy. Localized corrosion is suggested to be its corrosion pattern.     

Microstructure and enhanced mechanical properties of an Mg-10Gd-2Y-0.5Zr alloy processed by cyclic extrusion and compression

The evolution of microstructure and texture of an extruded GW102K Mg alloy processed by cyclic extrusion and compression (CEC) at 450 °C were investigated. Tensile tests were performed at room temperature and strain rate 5 × 10⁻³ s⁻¹. The results show that the microstructure was effectively refined, and the initial fiber texture became disintegrated and developed a new texture after 14 CEC passes. It was found that the strength and ductility were simultaneously increased compared with the as-extruded alloy. In particular, the elongation and yield strength were related in a line relationship having a positive slope. As the texture changed and texture intensity decreased, substantial grain refinement was observed. The hard second-phase particles were considered to be responsible for the uncommon properties of the GW102K alloy processed by CEC.     

The effect of extrusion speed on the structure and corrosion properties of aged and non-aged 6063 aluminum alloy

Extrusion is used in processing of Al alloy for consolidation, redistribution of reinforcements, and shape forming. The important parameter that controls the extrusion process is extrusion rate, which is a function of extrusion equipment and parameters. Homogenized AA6063 alloy billets were extruded at different ram speeds related to extrusion speed (3, 6, 10 mm s⁻¹) and then aged at 185 °C for 6 h. The extruded samples were studied for their corrosion, microstructure, and mechanical properties. The effects of extrusion speed and aging on the corrosion behavior of AA6063 were investigated using dynamic polarization and impedance techniques in 0.5 M NaCl aqueous solution. The surface structures were then characterized by means of surface profilometer. The electrochemical measurements showed that the decreasing ram speed for the aged sample improved the corrosion resistance. In addition, the aging improved the corrosion resistance of aluminum in 0.5 NaCl environments.     

Hot tensile properties and microstructural evolution of as cast NiTi and NiTiCu shape memory alloys

Hot tensile properties of as cast NiTi and NiTiCu shape memory alloys were investigated by hot tensile test at temperature range of 700–1100 °C using the strain rate of 0.1 s⁻¹. The NiTi alloy exhibited a maximum hot ductility at temperature range of 750–1000 °C, while the NiTiCu alloy showed it at temperature range of 800–1000 °C. It was found that at temperatures less than 750 °C, diffusion-assisted deformation mechanism was inactive leading to semi-brittle type of failure and limited ductility in both alloys. Also it was found that at temperature range of 800–1000 °C, dynamic recrystallization is dominant leading to high ductility. Likewise, the fracture surface of the specimens presenting the maximum hot ductility showed an ideal type of ductile rupture in which they gradually pulled out to a fine point. On the other hand, the decline in ductility occurred at the temperatures above 1000 °C was attributed to the liquid phase formation leading to interdendritic and intergranular type of fracture.     

Microstructures and mechanical properties of directionally solidified Ti–45Al–8Nb–(W,B, Y) alloys

Intermetallic Ti–45Al–8Nb–(W, B, Y) (at.%) alloys were directionally solidified at growth rates of 10–400 μm/s with a Bridgeman type apparatus. Microstructures and room temperature (RT) mechanical properties of the directionally solidified (DS) alloys were investigated. The microstructures with different segregation morphologies were observed at different growth rates. Fully lamellar (FL) microstructure evolves into a massive microstructure when the growth rate is up to 100 μm/s. Both the width of columnar grain and the interlamellar spacing decrease with increasing growth rate. Compressive properties were not proportional to the growth rates but closely related to the segregation morphologies. Only the DS alloy with columnar pattern of Al-segregation had tensile ductility. A better RT tensile plastic elongation level of 2% and yield strength 475 MPa were obtained at growth rate of 10 μm/s. Cracks propagated in transgranular mode predominantly. Larger elongated B2 particles produced in the interdendritic regions were detrimental to the tensile ductility of the DS alloy.     

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.     

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.     

Effect of isothermal extrusion parameters on mechanical properties of Al-Si eutectic alloy

In this paper, mechanical properties of a deformed Al-Si eutectic alloy processed by isothermal extrusion at temperature from 573 K to 773 K with reduction ratio from 25% to 85% were investigated at ambient temperature. The results showed that a banded structure composed of matrix region and accumulation region of second phase particles was formed and a few cracks were generated in particles and evolved to voids among particles. The tensile strength of test specimens ranged from 250 MPa to 400 MPa and was directly related with temperature from 623 K to 773 K. The elongation of test specimens ranged from 2.8% to 13.1%, and had a peak value at 673 K under each section reduction ratio. A reduction in elongation occurred at section reduction ratio larger than 75% because of particle bands splitting aluminum matrix severely. The effect of temperature on mechanical properties was more significant than that of section reduction ratio. Excellent balance between strength and ductility can be obtained by extrusion at temperature 623-723 K and section reduction ratio 40-70%.     

Tensile strength,ductility and fracture of magnesium-silicon alloys

Tensile tests were performed between 293–573 K in order to investigate the mechanical properties of cast and extruded Mg-Si alloys. For the cast materials, Mg-high Si ( 10 wt%) alloys showed lower values of the highest tensile strength at temperatures up to 373 K, as compared to pure Mg and Mg-low Si (<10 wt%) alloys, whereas the strength at 573 K increased with increasing Si content. The addition of aluminum and zinc to the alloys was effective in increasing the strength. The fact that the Mg-high Si alloys showed lower strength than the Mg-low Si alloys was because a high volume of Mg₂Si embrittled the Mg-Si alloys. Microstructural investigations revealed that the particles of Mg₂Si were coarse for the cast materials and fracture of the particles was caused by deformation. The mechanical properties of the cast materials were improved by hot extrusion. Microstructural refinement by hot extrusion was responsible for the improvement of the mechanical properties.     

Extrusion of vapour deposited Al–7·5Cr–1·2Fe (wt-%) alloy (RAE Alloy 72)

Abstract

Techniques and equipment were developed for the extrusion of vapour deposited RAE Alloy 72. The alloy was extruded at temperatures from 300 to 420°C and extrusion ratios from 2:1 to 25:1. Room and elevated temperature strengths and smooth S–N (stress–number of cycles to failure) fatigue properties were determined for a range of extrusions. The best extrusions gave room and elevated temperature strengths that were comparable to those of rapidly solidified aluminium alloys. The fatigue strength/tensile strength ratio of >0·5 was higher than would be expected for an aluminium alloy.

MST/1350     

Effect of Pd on microstructures and tensile properties of as-cast Mg-6Al-1Zn alloys

The effects of Pd on the microstructure and mechanical properties of Mg-6Al-1Zn alloys were investigated. Mg-6Al-1Zn-xPd (x = 0-6 wt.%) alloys were prepared using a permanent mould casting method. The microstructure of the as-cast alloys was characterized by the presence of Mg₁₇Al₁₂ and Al₄Pd phases. The volume fraction of the Al₄Pd phase was increased by the addition of 1-6 wt.%Pd but the volume fraction of the Mg₁₇Al₁₂ phases decreased. At room temperature, the tensile strength increased with increasing Pd addition up to 2 wt.%Pd, and the elongation to fracture decreased with a concomitant increase in the aggregation of the coarse Al₄Pd phase. At 150 °C, the tensile strength increased with the addition of Pd. Therefore, the room and elevated temperature tensile properties of as-cast Mg-6Al-1Zn alloys can be improved by Pd addition.     

Improvement of mechanical properties and corrosion resistance of biodegradable Mg–Nd–Zn–Zr alloys by double extrusion

Mg–Nd–Zn–Zr alloy is a novel and promising biodegradable magnesium alloy due to good biocompatibility, desired uniform corrosion mode and outstanding corrosion resistance in simulated body fluid (SBF). However, the corrosion resistance and mechanical properties should be improved to meet the requirement of the biodegradable implants, such as plates, screws and cardiovascular stents. In the present study, double extrusion process was adopted to refine microstructure and improve mechanical properties of Mg–2.25Nd–0.11Zn–0.43Zr and Mg–2.70Nd–0.20Zn–0.41Zr alloys. The corrosion resistance of the alloys after double extrusion was also studied. The results show that the microstructure of the alloys under double extrusion becomes much finer and more homogeneous than those under once extrusion. The yield strength, ultimate tensile strength and elongation of the alloys under double extrusion are over 270 MPa, 300 MPa and 32%, respectively, indicating that outstanding mechanical properties of Mg–Nd–Zn–Zr alloy can be obtained by double extrusion. The results of immersion experiment and electrochemical measurements in SBF show that the corrosion resistance of Alloy 1 and Alloy 2 under double extrusion was increased by 7% and 8% respectively compared with those under just once extrusion.     

The effect of cold and hot extrusion on the structure and mechanical properties of polypropylene

The direct extrusion of isotactic polypropylene through a 90° die at 23, 65, 95 and 120° C has been studied. As a result of extrusion, the tensile strength and the elastic modulus of the material are considerably increased whereas the ductility is decreased. Owing to the deformation of the material occurring in the extrusion process, the c-axis of the monoclinic unit cell aligns itself parallel to the extrusion direction and the lamellar structure is orderly arranged. The tensile strength and the orientation of the material extruded at higher temperatures are much higher than those obtained by extrusion at room temperature. The changes in the density and the mechanical properties resulting from extrusion have been explained in terms of the structural changes occurring in the material. A method has been suggested for estimating the spring back of extruded material.     

Anisotropy of thermal conductivity and mechanical properties in Mg–5Zn–1Mn alloy

The microstructure, texture, thermal conductivity and mechanical properties of the as-extruded Mg–5Zn–1Mn (ZM51) magnesium alloy were investigated on specimens with the extrusion direction (ED), the transverse direction (TD) and the normal to the extrude plane (ND), respectively. The results indicated that the thermal conductivity of ZM51 alloy at room temperature is 125 (W/m K), almost twice as high as other conventional commercial magnesium alloys, such as Mg–Al series and Mg–RE series. The effect of texture on anisotropy of mechanical properties and thermal conductivity has been analyzed. The strong crystallographic texture typical of Mg alloys results in much higher yield strength and tensile strength (UTS) in the extrusion direction, but higher ductility and thermal conductivity in the transverse direction.     

Elevated-temperature plasticity and mechanical properties of a rare earth-modified Mg-Zn-Al alloy

The elevated-temperature plasticity and flow behavior of an Er-modified, heat-resistant ZA73 alloy was evaluated by thermal simulation. The results showed that the addition of Er to ZA73 alloy notably improves the deformability and higher strain rate and temperature favors hot deformation. Bars with sound surface quality were successfully extruded at 350 °C and a strain rate of ~ 0.1 s^− 1. Furthermore, dynamic precipitation of nano-sized spherical τ phase was found to occur uniformly in the α-Mg matrix during hot extrusion, which is considered helpful to both strength and plasticity enhancement. The yield strength and ultimate tensile strength of the as-extruded bars reached 240-265 MPa and 355-360 MPa, respectively, while maintaining a large elongation rate of 18-19.5%.