Microstructure and mechanical properties of AZ31 Mg alloy after dual directional extrusion

A new dual directional extrusion (DDE) technique is applied on AZ31 Mg alloy at different extrusion ratios and temperatures by an extruder whose maximum load is 100t. In this experiment, the grain size is significantly reduced from 400 μm as cast to 6 μm as extruded when the extrusion ratio is 4.5; while at elevated extrusion ratio of 10.125, the grain size is reduced to 3 μm. The micro hardness, compressive ratio, elongation and yield strength are all improved a lot and decreased with the increase of extrusion temperatures (except 250 ℃).     

Influences of Y on the microstructures and mechanical properties of Mg-12Gd-1Zn-0.6Zr magnesium alloys

To develop Mg-Gd-Y based high-strength alloys and widen the application of magnesium alloys, the effects of Y addition on the microstructure and mechanical properties of Mg-12Gd-1Zn-0.6Zr alloy are investigated by using both optical and electron microscopy,X-ray diffraction (XRD),differential scanning calorimetric (DSC) analysis,and tensile test．The results indicate that adding 2%Y to the Mg-12Gd-1Zn-0.6Zr alloy does not cause an obvious change in the as-cast microstructure of the alloy. However,after adding 3%and 4%Y,the as-cast microstructure of the alloy is coarsened,and simultaneously the morphology of the secondary phases in the alloy is changed from the initial discontinuous fine network to thick skeleton-like frame. Furthermore,adding 2%-4%Y to the Mg-12Gd-1Zn-0.6Zr alloy can also refine the grains of the as-extruded alloy,and adding 2%and 3%Y can obtain higher refining efficiency than adding 4%Y. In addition,adding 2%-4%Y to the Mg-12Gd-1Zn-0.6Zr alloy can also effectively improve the ultimate tensile strength and yield strength of the as-extruded alloy,and the ultimate tensile strength,yield strength and elongation of the as-extruded alloy with the addition of 2%Y can reach 348.8 MPa,256.8 MPa and 14.7%,respectively.     

Effects of Nd content on microstructure andproperties of Mg-5.0Y-xNd-0.6Zr alloy

Effects of Nd content on the microstructure and mechanical properties of Mg-5.0Y-xNd-0.6Zr（x=0,1.0,1.8,2.6,3.4,4.2,mass fraction/%）alloy casts are investigated by optical microscopy(OM), scanning electron microscopy(SEM), differential scanning calorimetry(DSC), X-ray diffractometry(XRD) and tensile tests. The results reveal that increasing Nd content can refine the average grain size of alloys from 33.5 μm to 19.2 μm, reduce the number of Y atom in α-Mg and Mg24Y5 grain dispersed in the matrix, and increase β phase with the distribution of discontinuous network in crystal boundary. With the increase of Nd content, the tensile strength keeps rising first and subsequently falling, and the yield strength has a sharp increase at first and then gradually becomes constant, with the maximum values of 214.5 MPa and 102.8 MPa, respectively. The elongation and section shrinkage linearly decrease from 16.4% and 23.8% to 4.9% and 2.7% with the increase of Nd content. The mechanism of grain size refinement of Mg-5.0Y-xNd-0.6Zr alloys can be explained by Nd and Y enrichment in the forefront of solid-liquid interface during solidification process which enhances the supercooling of the solute rich zone and inhibits the crystal grain growth.     

Microstructure and properties characteristic during interrupted multi-step aging(T6I6) in Mg-Zn-Mn alloy

For researching the interrupted mutil-step aging techniques of Mg alloy, the effect T6I6 on microstructures and mechanical properties of the new alloy ZM61 is studied by XRD analysis, optional microscopy, electronic microscopy and EDS,TEM,hardness and machanical properties tests,etc. The results show that the T6I6 techniques, compared with T6, improve alloy strength more notably. The hardness of ZM61 after treated by T6I6 is 90HV, YS is 340MPa, UTS is 356 MPa, and the increased ratio of strength are 13% and 8% respectively. During the first step and second step of T6I6, only Mn continues to precipitate as α-Mn and forms more Mn simple particles. The grain boundaries of ZM61 alloy become clean during T6I6 treatment. The scope of strength increase sharply in third-step aging and the β precipitates distribute dispersively in the matrix while the strengthen effect been exerted drastically.     

Effects of Cu content on the microstructure and mechanical properties of AZ61 alloy

Microstructures and mechanical properties of AZ61 with Cu addition are investigated by optical microscope（OM）,X-ray diffraction analysis（XRD）,differential thermal analysis（DSC）,scanning electron microscopy(SEM) and energy spectrum analysis（EDS）.The results show that some ternary AlCuMg phases are observed along the grain boundaries and between dendrites in AZ61-xCu alloys, and they can refine the microstructure of as-cast alloys. Meanwhile, with the addition of Cu,the quantity and the size of β-Mg17Al12 decrease. As Cu content increasing, the strength of as-extruded alloys increase first and then decrease.The elongation has no obvious decrease until Cu content reaches 1.5%. AZ61-1Cu alloy has optimum combination mechanical properties,with σ0.2=230 MPa,σb=321 MPa and δ=9.7%,respectively.When Cu content is 1.5%, the coarse AlCuMg phase splits the matrix and deteriorates mechanical properties.     

Microstructure and mechanical properties of extruded Mg-9Li-3Al-xSr alloys

The microstructure and mechanical properties of extruded Mg-9Li-3Al-xSr (LA93-xSr, x=0, 1.5, 2.5, 3.5 wt%) alloys are investigated by SEM, EDS, XRD, TEM and mechanical property test. The influence of Sr content on microstructure and mechanical properties the extruded alloys is discussed. The results show that LA93-xSr alloys contain both α-Mg (hcp) and β-Li (bcc) matrix phases. The effect of Sr on the grain size of the extruded alloys is not significant. The addition of Sr leads to the formation of intermetallic compound (Al4Sr), which is mainly distributed along the α/β interface and appears fibrous structure along the extrusion direction. The mechanical properties of alloys initially enhance and then decrease while the elongation declines with the increase of Sr content. When Sr addition is 2.5wt%, the extruded Mg-9Li-3Al-2.5Sr (LAJ932) alloy exhibits a favorable combination of strength and ductility with an ultimate tensile strength of 235.2 MPa, yield strength of 220.6 MPa and an elongation of 19.4%. Microstructure evolution during extrusion is governed by deformation induced grain refinement in the α-Mg phase whereas dynamic recrystallization occurs in the β-Li phase.     

Effect of thermo-mechanical treatment on microstructure and mechanical property of 2197 Al-Li alloy

For thermo-mechanical treated 2197 alloy of various states, effects of thermo-mechanical treatment on the mechanical properties and microstructure of 2197 alloy are studied through analyzing the mechanical properties in tensile tests and observing the microstructures by TEM observation. Results show that the dominating precipitated phase of peak-aged 2197 alloy during thermo-mechanical treatment is T1 phase,the size of which is 50~150 nm. The precipitation and growth of T1 phase are accelerated due to the excellent nucleation sites of heterogeneous nucleation for T1 phase offered by thermo-mechanical treatment,therefore,the time for 2197 alloy to reach the peak-aged state is shortened. The strength of 2197 alloy for peak-aged state is increased through thermo-mechanical treatment because the strengthening effect of T1 phase with higher aspect ratio is bigger than that of δ′ and θ′ phases.     

Effects of Nd on microstructure and corrosion behavior of AJ61 magnesium alloy

AJ61-xNd magnesium alloys are prepared in vacuum furnace under the protection of argon atmosphere and the effect of Nd content on microstructure of the test alloy is studied. The corrosion behavior of AJ61-xNd alloys in 3.5% NaCl aqueous solution is investigated by static weight-loss test and polarization curve measurement. The results indicate that with the addition of Nd, binary Al2Nd phase and Al3Nd phase are formed in the alloy, meanwhile, grain sizes are greatly reduced with the addition of Nd and the refinement effect on the test alloy is the best when the mass fraction of Nd is 0.5%. It is found that due to the addition of Nd, the corrosion rate and corrosion current of AJ61 magnesium alloy can be significantly reduced, the equilibrium potential and corrosion potential of the test alloy can be enhanced substantially. The corrosion resistance of AJ61 magnesium alloys is improved a lot with the Nd addition. The AJ61-0.5Nd magnesium alloy has the best corrosion resistance behavior.     

早果、矮化、抗逆苹果砧木Y系的选育研究

为选育具有本土适应性的苹果矮化砧木,以中国原生的种质资源——野生晋西北山定子为试材,通过田间观察和综合评价,以其实生苗为自根砧嫁接苹果品种,以早花、早果为筛选指标进行初选,以连续开花和结果性能、耐旱性、抗寒性、接穗品种果实品质为主次顺序筛选指标,进一步逐级筛选,进行复选,以八棱海棠为自根砧,复选出的植株自根砧萌蘖苗为中间砧嫁接苹果品种,以矮化性、植株生长势、连续开花和结果性能、耐旱性、抗寒性、接穗品种果实品质为主次顺序筛选指标逐级筛选,进行决选。结果表明,以初选出的砧木群体(定名为Y系)作为自根砧的嫁接植株,早花早果特性和连续开花结果能力极为突出,矮化性状明显,抗寒、抗旱性较强;以决选出的4个优系为中间砧的嫁接植株,除具有Y系嫁接植株基本特性外,果实品质较好。Y系是具有较强的矮化、开花结果、抗寒、抗旱性能的苹果砧木群体,具有很大的苹果矮化砧木选育潜力;4个优系的矮化、开花结果、耐旱、抗寒性能较强,其中,Y-1(原名Y-B030)为矮化砧木,Y-2(原名Y-B094)为极矮化砧木,Y-3(原名Y-B007)为半矮化砧木,均已通过区试及品种审定。     

Mechanical property prediction model of AZ31 magnesium alloys based on an artificial neural network with parameter optimization

The tensile strength, yield strength and elongation of AZ31 magnesium alloys on different annealed conditions are tested by mechanical properties experiments. A model of corresponding mechanical properties is built by applying artificial neural network, and it is optimized by a new method,namely all permutations and combinations training of parameters. The results show that the network model has an excellent performance, which is based on optimal parameters obtained from all permutations and combinations training. Compared with traditional model, whose parameters are obtained from conventional heuristic, the improved model has higher average correlation coefficient and lower average error. Therefore, it can predict the mechanical properties of AZ31 magnesium alloy on different annealed conditions more accurately.     

Effect of nitrogen on microstructure and properties of SWRH82B wire rod

The microstructure, mechanical properties, tensile fractures and the precipitation of the second phase of vanadium microalloyed wire rods with different nitrogen contents are studied by hydraulic universal testing machine, scanning electron microscopy(SEM) and transmission electron microscopy(TEM) . The results show that the interlamellar spacing of pearlite is smaller in high nitrogen steel; the high nitrogen steel has higher yield strength, tensile strength and lower elongation and reduction of area; there are more inclusions on the tensile fracture surfaces of the high nitrogen steel; and in high nitrogen steel, the size of precipitation, mainly precipitating at dislocation or the boundary of austenite, is finer than that of low nitrogen steel, what is more, fine V(C,N) particles are concluded in the precipitations.     

增施不同的有机物质对烤烟物理性状和氨基酸含量的影响

以河南南阳烤烟为材料研究了在常规措施（CK）下增施不同的有机物质对烤烟物理性状和氨基酸含量的影响。结果表明：（1）与常规施肥相比,增施发酵后豆浆的烟叶叶片厚度、平衡含水率、叶质重、拉力和抗张强度增加,而填充值下降,增施芝麻和豆参的处理呈现出相反的趋势,增施香油的处理变化不明显。（2）烤后烟叶氨基酸总的含量以增施豆制品的较高,其次是增施芝麻制品的处理。各处理以谷氨酸、脯氨酸、天冬氨酸、亮氨酸、丙氨酸、甘氨酸、缬氨酸、赖氨酸、苯丙氨酸等含量较高,其含量约占氨基酸总量的75%,且脯氨酸、天冬氨酸、苏氨酸、丙氨酸等几种成分在处理F、E和D中的含量较高,缬氨酸、酪氨酸、苯丙氨酸等以处理E中的含量较高。（3）增施的有机物质种类不同,其效果也有所不同,其中以增施发酵后的豆浆的两个处理最好,其次是增施豆参,增施芝麻和香油的两个处理效果稍差。     

污泥与城市生活垃圾混填的力学特性及稳定性

工业污水和生活污水排放量日益增多,污水处理厂污泥产量日趋加大,污泥填埋关键技术问题已成为当今环境工程以及环境岩土工程的热点问题之一。污泥和垃圾混合填埋在其他国家已得到应用,但由于目前中国关于污泥及其城市生活垃圾混合样的基础性室内试验成果不多,对污泥与城市垃圾混合样的工程力学特性及其混合填埋的适宜比例等不甚了解,从而导致中国污泥垃圾混合填埋工程事故频繁发生。对不同配比的污泥与城市生活垃圾混合样进行了固结压缩实验、三轴固结不排水实验、无侧限抗压强度实验,得出污泥与城市生活垃圾混合样的工程力学特性;同时,用ANSYS数值模拟方法,对不同配合比的污泥城市生活垃圾混合填埋边坡的稳定性进行分析,从而对污泥与城市生活垃圾混合填埋的适宜配合比及其稳定安全问题提出理论支撑。     

G550高强冷弯薄壁槽钢受弯构件力学性能与设计方法

为了研究高强冷弯薄壁槽钢受弯构件的力学性能和设计方法,对3种板件加劲形式的G550高强冷弯薄壁型钢槽形截面受弯构件进行了试验研究和有限元参数分析。结果表明,板件加劲形式对高强冷弯薄壁槽钢受弯构件屈曲模式和受弯承载力有显著影响,翼缘V形加劲比腹板V形加劲能够更有效地提高构件抗弯承载力,构件抗弯承载力的变化规律与屈曲模式有关。根据有限元参数分析结果,在已有直接强度法基础上回归出适用于高强冷弯薄壁槽钢受弯构件的直接强度法修正公式。