Compressive and energy absorption properties of closed-cell magnesium foams

The quasi-static compressive mechanical behavior and deformation mechanism of closed-cell magnesium foams were studied, and the ef- fects of the density of magnesium foams on the compressive and energy absorption properties were also discussed. The results show that the compressive process of closed-cell magnesium foams is characterized by three deformation stages： linear elastic stage, collapsing stage and densification stage. At the linear elastic stage, the peak compressive strength （t70） and Young＇s modulus （E0） increase as the density increases Magnesium foams can absorb energy at the collapsing stage. In a certain strain range, the energy absorption capacity also increases as the density of magnesium foams increases.

Development of open-porosity magnesium foam produced by investment casting

High-porosity,open-cell AZ91 magnesium alloy foams of two pore sizes were fabricated by means of investment casting technology,using PUR foam patterns.Foam casting variables such as pressure,mould temperature and metal pouring temperature were thoroughly investigated to define the most optimal casting conditions.The mechanical properties of the fabricated foams were measured in compression tests.A potential application for the foams considered is temporary bioresorbable bone implants,therefore the mechanical properties of the foams were compared with those of cancellous bone tissue.Foams with smaller pore size and lower porosity(20 PPI and 80%±87%)exhibited mechanical properties in the lower regions of the cancellous bone property range(Young’s modulus 36.5±77.5 MPa),while foams with higher pore size and porosity(10 PPI and~90%)were found to have insufficient compression strength(Young’s modulus 11.65±23.8),but thickening their walls and lowering their porosity below 90%yielded foams with Young’s modulus between 36.5 and 77.5 MPa.Foam fractures were also investigated to determine their collapse mechanism.A series of corrosion tests in stimulated body fluid was carried out to determine their applicability as a biomaterial.The Plasma Electrolytic Oxidation(PEO)process was used in a feasibility study to examine the microstructure and chemical composition of foams with protective coating.

Microstructure and Properties of Cement Foams Prepared by Magnesium Oxychloride Cement

Microstructural features including pore size distribution, cell walls and phase compositions of magnesium oxychloride cement foams（MOCF） with various MgO powders and water mixture ratios were studied. Their infl uences on compressive strength, water absorption and resistance of MOCF were also discussed in detail. The experimental results indicated that moderate and slight excess MgO powders（MgO/MgCl2 molar ratios from 5.1 to 7） were beneficial to the formation of excellent microstructure of MOCF, but increasing water contents（H2O/MgO mass ratios from 0.9 to 1.29） might result in opposite conclusions. The microstructure of MOCF produced with moderate and slight excess MgO powders could enhance the compressive strength, while serious excess MgO powders addition（MgO/MgCl2 molar ratios = 9） would destroy the cell wall structures, and therefore decrease the strength of the system. Although MOCF produced with excess MgO powders could decrease the water absorption, its softening coefficient was lower than that of the material produced with moderate MgO powders. This might be due to the instability of phase 5, the volume expansion and cracking of cell walls as immersed the sample into water.

Heat transfer characteristics of lost foam casting process of magnesium alloy

Effects of vacuum, pouring temperature and pattern thickness on the heat transfer of magnesium alloy lost foam casting(LFC) process were explored. The results indicate that without vacuum a positive thermal gradient from the gate to the end of the casting was formed immediately after the mold filling. The average temperature of the casting, the temperature gradient and solidification times increase significantly with pouring temperature and pattern thickness. Vacuum plays a quite different role in the heat transfer during mould filling and solidification periods: it significantly increases the cooling rate of the filling melt, but decreases the cooling rate of the casting during solidification period. The temperature of the liquid metal drops sharply and varies greatly with no apparent mode in the casting after the mold filling. The amplitude of temperature fluctuations in the casting increases with vacuum, pouring temperature and pattern thickness. The average temperature increases with pouring temperature and pattern thickness, but less rapidly than that without vacuum. The effect of vacuum on the solidification times of castings is found to depend on pouring temperature, vacuum makes solidification times increase greatly at high pouring temperature, while decreases slightly at low pouring temperature.

Microstructure and mechanical properties of magnesium alloy prepared by lost foam casting

The microstructure and mechanical properties of AZ91 alloy prepared by lost foam casting（LFC） and various heat treatments have been investigated. The microstructure of the AZ91 alloy via LFC consists of dominant α-Mg and β-Mg17Al12 as well as a new phase Al32Mn25 with size of about 550 μm, which has not been detected in AZ91 alloy prepared by other casting processes. The tests demonstrate that the as-cast mechanical properties are higher than those of sand gravity casting because of chilling and cushioning effect of foam pattern during the mould filling. The solution kinetics and the aging processes at different temperatures were also investigated by hardness and electrical resistivity measurements. The kinetics of aging are faster at the high temperature due to enhanced diffusion of atoms in the matrix, so the hardness peak at 380 ℃ occurs after 10 h; while at the lower aging temperature（150 ℃）, the peak is not reached in the time（24 h） considered.

Study on typical hole defects in AZ91D magnesium alloy prepared by low pressure lost foam casting

The hole defects can easily occur in magnesium alloy castings that are prepared by low pressure lost foam casting(LP-LFC)process when the process parameters such as vacuum,pouring temperature and f illing velocity are not properly selected.In this study,the forming mechanism of the hole defects in AZ91D magnesium castings by LP-LFC process was investigated.The shape,location and surface appearance of the hole defects were observed using optical microscopy and scanning electron microscopy,and the chemical composition on the surface of the holes was analyzed using energy spectrometer.The result indicates that there are two types of hole defects,i.e.,the pyrolysis products related hole defects,including concentrative hole and blow hole defects,and slag related hole defects.The concentrative hole and the blow-hole defects were formed either by the liquidEPS degradation products entrapped in the molten metal under the condition that the pouring temperature is equal to or lower than 730℃,or by the hindered transport of EPS pyrolysis products.Some irregular shape hole defects were caused by slag or by coating slough entrapment when the pouring temperature is equal to 750℃and the f illing velocity is equal to or greater than 100 mm·s-1.To reduce or eliminate the hole defects,the vacuum and f illing velocity must be properly chosen to ensure that the metal front prof ile exhibits convex shape and in laminar current state,and the pouring temperature should be just high enough to ensure that the molten melt has adequate heat energy to complete the foam pyrolysis and to fully occupy the mould.For AZ91D magnesium castings in this study,the parameters should be 730℃pouring temperature,0.02-0.03 MPa vacuum and 80mm·s-1f illing velocity.

外加剂对硫氧镁水泥泡沫混凝土性能影响

该文研究磷酸三钠、葡萄糖、有机酸C、有机酸盐D四种外加剂复掺对硫氧镁水泥泡沫混凝土抗压强度和耐水性的影响。并采用XRD、SEM表征硫氧镁水泥泡沫混凝土试样的物相组成和微观结构。结果表明,适当掺量的四种外加剂都能提高硫氧镁水泥泡沫混凝土抗压强度及耐水性,有机酸C对硫氧镁水泥泡沫混凝土抗压强度影响较大,有机酸C掺量为0.6%时,试块28 d抗压强度达到1.91 MPa;磷酸三钠可以有效改善硫氧镁水泥泡沫混凝土耐水性,当磷酸三钠掺量0.6%时,试块软化系数达0.8;复掺外加剂试样强度与耐水性得到提升,其28 d抗压强度达到2.1 MPa,是不掺外加剂试样的1.58倍,其软化系数达0.92。

基于熔体发泡法制备泡沫镁合金工艺优化及性能研究

为提升泡沫镁材料性能,研究泡沫镁制备工艺中Al元素的加入及发泡时间对泡沫镁基体性能和孔结构的影响,进而对泡沫镁材料力学性能的影响。选用纯镁(Mg)、纯铝(Al)和钙(Ca)粒作为基本材料,采用熔融铸造法制备出Mg-10Al-3Ca基体合金。以该合金为原料,分别添加2wt.%的SiC和MgCO_(3)颗粒作为增黏剂和发泡剂,在常温常压条件下,在以熔体发泡法制备泡沫镁的过程中通过优化发泡时间,成功制备出孔隙率在56.56%~73.15%范围内的泡沫镁材料。采用扫描电子显微镜(SEM)、微区EDS能谱分析(EDS)、X射线衍射(XRD)等表征方法对制备的泡沫镁试样进行微观相组成分析,并通过万能试验机对试样进行力学性能测试。结果表明,通过添加Al元素制备的Mg-10Al-3Ca基体合金的抗压强度达到了303.35 MPa;通过优化发泡时间所制备的泡沫镁材料最大抗压强度为30.55 MPa、孔隙率为56.56%、吸能能力达到18.06 MJ/m3,具有良好的孔隙结构和性能。

发泡-自发凝固浇注法制备镁铝尖晶石质多孔材料

为了提高热工窑炉的热效率,降低热能损耗,以工业级中档镁砂细粉(d50=34.2μm)、煅烧氧化铝粉(d50=3.4μm)为原料,油酸钾为发泡剂,羧甲基纤维素钠为稳泡剂,异丁烯与马来酸酐交替共聚物(ISOBAM-104,简称“IB”)为固化剂,采用发泡-自发凝固浇注法制备镁铝尖晶石质多孔材料,研究了IB加入量(外加质量分数分别为0、0.1%、0.2%、0.3%和0.4%)对料浆和1500℃保温3 h烧后试样性能的影响。结果表明:1)随IB加入量增加,料浆的膨胀比减小,Zeta电位的绝对值先增大后减小,烧后试样的显气孔率减小,体积密度增大,常温耐压强度先升高后降低,气孔分布由紧密堆积变为独立分散,孔壁增厚,热导率先增大后减小。2)当IB加入量为0.3%(w)时,Zeta电位为-52.6 mV,料浆最稳定;烧后试样的常温耐压强度最大,为32.7 MPa,显气孔率为54.4%,体积密度为1.63 g·cm^(-3),热导率为0.205 W·m^(-1)·K^(-1)(350℃);平均气孔尺寸最小,为46.8μm,综合性能最佳。

Low-frequency damping behavior of closed-cell Mg alloy foams reinforced with SiC particles

The damping properties of an Mg alloy foam and its composite foams were investigated using a dynamic mechanical thermal analyzer. The results show that the loss factors of both the Mg alloy and its composite foams are insensitive to temperature and loading frequency when the temperature is less than a critical temperature Tcrit. However, it increases when the temperature exceeds the Tcrit values, which are 200 and 250°C for the Mg alloy foam and the Mg alloy/SiCp composite foams, respectively. The Mg alloy/SiCp composite foams exhibit a higher damping capacity than the Mg alloy foam when the temperature is below 200°C. By contrast, the Mg alloy foam exhibits a better damping capacity when the temperature exceeds 250°C. The variation in the damping capacity is attributed to differences in the internal friction sources, such as the characteristics of the matrix material, abundant interfaces, and interfacial slipping caused by SiC particles, as well as to macrodefects in the Mg alloy and its composite foams.

Preparation of Light-weight Spinel Refractories by Foaming-gel Process

Light-weight magnesium -aluminate spinel materi- als were prepared by foaming-gel process with polyalumi- nium chloride （PAC） as gel. Effect of solid loading in initial slurry on microstructure, porosity, pore size distri- bution, thermal conductivity and mechanical properties was investigated. The results show that the bulk density of the light-weight magnesium -aluminate spinel mate- rials is in the range of O. 7 1.2 g cm-3 ; pore size distribution curves show single-peak characteristics and the mean pore size is in the range of 30. 83 - 61.37 μm ; with the increase of solid loading, the linear shrinkage of the green body during firing and the permanent change in dimensions on heating at l 600 ℃ for 3 h de- crease, but the bulk density increases, the mechanical properties increase obviously; the maximum compressive strength and bending strength reach 35. 25 MPa and 9. 92 MPa, respectively, while the bulk density is 1. 16 g · cm ; and the thermal conductivity at 1 000 ℃ tea- ches 0. 371 W · m-1 . K-1 while the bulk density is O. 7 -3 g · cm

Effect of vacuum on solidification process and microstructure of LFC magnesium alloy

Lost foam casting (LFC) is regarded as a cost-effective, environment-friendly vital option to the conventional casting process for production of near-net shape castings with high quality. Effect of vacuum on the solidification process and microstructure of LFC magnesium alloy were explored. The results indicate that vacuum plays a very important role in the heat transfer during mould filling and solidification periods, it increases the cooling rate of the filling melt, but greatly decreases the cooling rate of the casting during solidification period, and the solidification time of the casting is greater than that without vacuum. The microstructure of LFC magnesium alloy is rather coarse. Compared with that without vacuum, the microstructure of the LFC magnesium alloy under vacuum is more refined and has less precipitatedβ-phase, which is formed at the grain boundry and around the Al-Mn compound particle.

Non-flux purification behavior of AZ91 magnesium alloy

The effects of non-flux purification techniques on the mechanical properties and microstructure of AZ91 magnesium alloy were investigated by ICP,OM,XRD and SEM.The results show that Ar spraying with high flow rate could remove non-metallic inclusions and improve the mechanical properties of AZ91.The alloy obtains the best properties after argon spraying for 30 min at the melt temperature of 740 °C.The ceramic foam filter(CFF) could effectively improve the ultimate tensile strength and elongation of AZ91 alloy,especially the elongation,which increase with increasing pores per inch(ppi) and the thickness of CFF.Non-flux purification does not change the microstructure of AZ91 alloy.However,filtration has a certain effect on the fracture pattern of AZ91 alloy.To improve the mechanical properties effectively,both filtration and gas spraying should be utilized together.

Status quo and development trend of lost foam casting technology

Lost foam casting(LFC)technology has been widely applied to cast iron and cast steel.However,the development of LFC for Al and Mg alloys was relatively slower than that for cast iron and cast steel.The application of LFC to Al and Mg alloys needs more effort,especially in China.In this paper,the development history of LFC is reviewed,and the application situations of LFC to Al and Mg alloys are mainly discussed.Meanwhile,the key problems of LFC for Al and Mg alloys are also pointed out.Finally,the prospects for LFC technology are discussed,and some special new LFC technologies are introduced for casting Al and Mg alloys.In future,the development trends of green LFC technology mainly focus on the special new LFC methods,metal material,coating,heat treatment,new foam materials as well as purification technology of tail gas,etc.

泡沫掺量对超轻质硫氧镁基泡沫混凝土性能的影响

硫氧镁水泥具有轻质、导热系数低、耐火等优点,将其制备成泡沫混凝土并应用于建筑外墙保温系统具有巨大的市场潜力。本文通过加入高稳定改性泡沫来调控超轻质硫氧镁基泡沫混凝土的密度,并结合扫描电子显微镜(SEM)、光学显微镜(OM)等测试研究了气孔结构的变化,探究了密度和孔结构变化对超轻质硫氧镁基泡沫混凝土抗压强度和导热系数的影响。结果表明:随着高稳定改性泡沫掺量的增加,超轻质硫氧镁基泡沫混凝土的气孔数量增多且平均孔径明显减小,密度逐渐减小,抗压强度逐渐降低;当泡沫掺量为250%(质量分数)时,超轻质硫氧镁基泡沫混凝土的密度降低至88.33 kg/m^(3),导热系数降低至0.0382 W/(m·K)。

利用H_(2)O_(2)发泡和碳化养护改善RMFC的固碳、力学和保温隔热性能

开发新型低碳胶凝材料替代高能耗高碳排放的硅酸盐水泥是水泥与建筑行业碳减排的重要途径之一。通过H_(2)O_(2)发泡和CO_(2)养护活性氧化镁水泥(Reactive magnesium oxide cements,RMC),制备了一种可快速大量固碳且具有保温隔热性能的活性氧化镁泡沫混凝土(Reactive magnesium oxide foam concrete,RMFC),并研究得到了各因素对材料发泡、固碳、力学及隔热性能的影响规律及作用机理。考察了水灰比、H_(2)O_(2)掺量和H_(2)O_(2)预热温度对RMC浆体发泡效果的影响规律;研究了孔隙率、养护条件和碳化时间对RMFC碳化行为的作用效果;分析了孔隙率、养护条件与碳化时间对RMFC力学性能和保温隔热性能的作用机理。研究表明:通过适当提高水灰比延长RMC浆体初凝时间、预热H_(2)O_(2)提高其分解速率,可制备得到孔隙率较高的RMFC;提高孔隙率、增加CO_(2)浓度和降低碳化温度可显著提升固碳率,碳化温度不同还导致碳化产物有所不同;降低孔隙率或提高碳化水平可得到强度较高但导热系数较大的RMFC;试验中制备得到了容重635~1335 kg/m^(3)、抗压强度3.75~9.1 MPa,导热系数0.32~0.49 W/(m·K)的RMFC。本工作提出的RMFC制备方法具有显著的固碳效果,试验中每吨RMC固定CO_(2)的最大值为0.42 t,以其替代硅酸盐水泥泡沫混凝土可助力水泥与建筑行业实现“碳达峰、碳中和”。

粉煤灰掺量对硫氧镁泡沫水泥性能的影响

研究了改变粉煤灰的掺量对硫氧镁泡沫水泥性能的影响,试验结果表明,掺入定量的粉煤灰后,混凝土性能将得到明显提高,且随粉煤灰掺量的变化而变化。

用于泡沫混凝土的磷酸镁水泥基胶凝材料研究

以偏高岭土、玻化微珠、粉煤灰复合的矿物掺合料等量替代氧化镁,外掺超细SiO_(2),测试磷酸镁水泥净浆的凝结时间、流动性能、力学性能,研究相应胶砂试块的耐水性能,获得一种适用于制备泡沫混凝土的磷酸镁水泥基胶凝材料。结果表明:当偏高岭土、玻化微珠、粉煤灰以质量比7∶1∶2复合(等量替代30%氧化镁),外掺1%超细SiO_(2)时,磷酸镁水泥净浆与砂浆的3 d、7 d、28 d抗压强度、耐水性等均高于对照组无掺合料MPC;使用其制备泡沫混凝土,能够有效解决密度降低过程中的膨胀开裂问题,可以获得密度为500~600 kg/m^(3)的磷酸镁水泥基泡沫混凝土,其7 d抗压强度大于4.0 MPa,强度保留系数大于0.85,力学性能和耐水性能远远优于无掺合料的磷酸镁水泥基泡沫混凝土。

憎水剂对硫氧镁水泥泡沫混凝土性能的影响研究

以硫氧镁水泥为胶凝材料、膨胀珍珠岩为轻质骨料,采用物理发泡工艺制备干密度为600 kg/m3的发泡混凝土,以此分析研究憎水剂对硫氧镁水泥发泡混凝土抗压强度、抗折强度、体积吸水率、耐水软化系数及憎水率的影响。研究结果表明:掺加憎水剂,基本不影响泡沫混凝土的抗压强度和干密度,综合考虑最佳掺量为轻烧氧化镁粉质量份数的2.0%。

闭孔泡沫镁材料静动态压缩力学性能与吸能特性

实验研究了闭孔泡沫镁材料静动态压缩过程的力学性能和吸能特性。得到了材料在准静态压缩下的微观变形特点,不同应变率条件下的压缩应力应变关系曲线及其特征。用单位体积的吸能W来表征材料的吸能特性,分析了在静动态条件下孔径和相对密度对泡沫镁材料的应力应变关系和单位体积吸能的影响规律。结果表明:孔径对闭孔泡沫镁力学性能和吸能特性影响显著,存在一个适中的孔径范围,此时泡沫镁的性能最优;随着相对密度增加,屈服强度和单位体积吸能W显著增加。研究结果可为多孔材料动态破坏研究和材料及工程设计提供理论依据和参考。