Towards developing Mg alloys with simultaneously improved strength and corrosion resistance via RE alloying

Magnesium(Mg)alloys have received an increasing interest in the past two decades for their tremendous application potential.The strength and corrosion resistance levels of common Mg alloys are still relativity low,and especially they are to be improved simultaneously.The addition of rare earth(RE)to Mg alloys is believed to be beneficial for both the strength and corrosion resistance,and some RE-modified traditional Mg alloys have been studied and some new RE-containing Mg alloys have been developed by now.However,further simultaneous improvements in both strength and anti-corrosion require a better understanding of the behavior and mechanism of RE in Mg alloys.In this review,the common influence mechanisms of RE on mechanical and anti-corrosion properties of Mg alloys are summarized,and the latest research progress of RE-containing Mg alloys with simultaneously improved strength and corrosion resistance are introduced.It is demonstrated that the research on high-strength and high corrosion resistant RE-containing Mg alloys is still immature,and some opinions and suggestions are put forward for the synergetic improvement of the strength and corrosion resistance of Mg alloys,so as to contribute to the further development of Mg alloys with higher performance.

Comparisons of microstructure homogeneity,texture and mechanical properties of AZ80 magnesium alloy fabricated by annular channel angular extrusion and backward extrusion

This paper provided an efficient single pass severe plastic deformation(SPD)method,annular channel angular extrusion(ACAE),for fabricating AZ80 magnesium alloy shell part.The effect of ACAE process on the microstructure homogeneity,texture,and mechanical properties of extruded part was experimentally investigated.For comparison,conventional backward extrusion(BE)was also conducted on processing AZ80 part with same specification.The results showed that ACAE process has a better capacity to refine the microstructure and dramatic improve the deformation homogeneity of the extruded part than BE process.Due to two strong shear deformations were implemented,ACAE process could also concurrently modify the basal texture more notably than BE process.In particular,a bimodal texture was found in ACAE extruded part,which was greatly related to the enhanced synergetic action of basal slip and secondary<c+a>slip caused by the effective shear stress.More uniform and superior hardness along the thickness and height of part were achieved via ACAE process.Further surveying of tensile tests also showed that the part fabricated by ACAE process exhibited significantly higher and far more homogeneous tensile properties with an excellent balance of strength and ductility.The remarkable enhanced tensile properties of ACAE extruded part could be primarily attributed to the significant grain refinement,which provided a powerful grain boundary strengthening effect and meaningfully suppressed the development of twin-sized cracks during tensile deformation.It was established that ACAE process seemed to be a very promising single pass SPD method for manufacturing Mg-based alloy shell parts with more homogeneous microstructure and superior performance.

Effect of ageing treatment on microstructures,mechanical properties and corrosion behavior of Mg-Zn-RE-Zr alloy micro-alloyed with Ca and Sr

Effects of ageing treatment on the microstructures,mechanical properties and corrosion behavior of the Mg-4.2Zn-1.7RE-0.8Zr-xCa-ySr[x=0,0.2(wt.%),y=0,0.1,0.2,0.4(wt.%)]alloys were investigated.Results showed that Ca or/and Sr additions promoted the precipitation hardening behavior of Mg-4.2Zn-1.7RE-0.8Zr alloy and shortened the time to reaching peak hardness from 13 h to 12 h.The maximum hardness of 77.1±0.6 HV for the peak-aged Mg-4.2Zn-1.7RE-0.8Zr-0.2Ca-0.2Sr alloy was obtained.The microstructures of peak-aged alloys mainly consist ofα-Mg phase,Mg_(51)Zn_(20) phase and ternary T-phase.The Zn-Zr phase is formed within theα-Mg matrix,and the Mg_(2)Ca phase is formed near T-phase due to the enrichment of Ca in front of the solid-liquid interface.Furthermore,fine short rod-shapedβ′1 phase is precipitated within theα-Mg matrix in the peak-aged condition.The peak-aged Mg-4.2Zn-1.7RE-0.8Zr-0.2Ca-0.2Sr alloy exhibits optimal mechanical properties with an ultimate tensile strength of 208 MPa,yield strength of 150 MPa and elongation of 3.5%,which is mainly attributed to precipitation strengthening.In addition,corrosion properties of experimental alloys in the 3.5wt.%NaCl solution were studied by the electrochemical tests,weight loss,hydrogen evolution measurement and corrosion morphology observation.The results suggest that peak-aged alloys show reduced corrosion rates compared with the as-cast alloys,and minor additions of Ca and/or Sr improve the corrosion resistance of the Mg-4.2Zn-1.7RE-0.8Zr alloy.The peak-aged Mg-4.2Zn-1.7RE-0.8Zr-0.2Ca-0.2Sr alloy possesses the best corrosion resistance,which is mainly due to the continuous and compact barrier wall constructed by the homogeneous and continuous second phases.

Effect of Auxiliary Gas Flow Parameters on Microstructure and Properties of Ta Coatings Prepared by Three-Cathode Atmosphere Plasma Spraying

Based on the three-cathode plasma spraying system,tantalum(Ta)coatings were pre-pared on the substrate of CuCrZr alloy.The effects of different auxiliary gas(helium)flow rates on the microstructure,phase composition,mechanical and wear resistance properties of Ta coatings were studied.The results showed that the oxidation degree of the coatings decreases first and then increases with the increase of the auxiliary gas flow.When the auxiliary gas flow rate is 70 L·min-1,the oxidation degree of the coating is the lowest,minimum value of the porosity is 0.21%,and the bonding strength reaches the maximum,59.3 MPa.At this time,the coating wear rate is 0.0012 mm^(3)·N^(-1)·m^(-1)with the best wear resistance.This indicates that the auxiliary gas flow has an important influence on the quality and surface mechanical properties of tantalum coating.

Explosive compaction of CuCr alloys

The production of CuCr alloys utilizing explosive compaction was studied. Mixture powders of CuCr alloys placed in tubes with a dimension of d14.0 mm×21.4 mm can be compacted using explosive pads of 16.5 mm or 22.5 mm. Thicker pads of explosive make the compacts more porous. The effects of the ratio of m e/m p, ratio of m e/(m p+m t) and impact energy on the density of compacts were similar, they were chosen to control explosive compaction, respectively. When adequate value of the parameters m e/m p, m e/(m t+m p) and impact energy of unit area of tube was chosen, high density(7.858 g/cm 3), high hardness(HB189) and low conductance (13.6 MS/m) of CuCr alloys could be made by explosive compaction. The general properties of CuCr alloys by explosive compaction are similar to those of CuCr alloys by traditional process.

Numerical Simulation and Experimental Research on Penetration of Composite Ceramic Armor by Rod Projectile

The performance of composite ceramic armor penetrated by rod projectile was studied by both numerical simulation and experiment.The penetration and damage mechanisms of the projectile-armor after high-speed collision were also observed by high-speed photography.The experimental results showed that the ballistic performance of composite ceramic armor was highly affected by the density,hardness and toughness of bulletproof ceramic.The flow stress of the failed bulletproof ceramic is not only related to the pressure but also related to the strain rate.The phenomenological method based on Bodner-Partom ceramic model was introduced to derive the growth rate of damage.Numerical simulation results show good agreement with the experimental results.

Microstructure and Mechanical Properties of TiB_2-Al_2O_3 Composites

Effects of Al2O3 and Ni as the additives on the sinterability, microstructure and mechanical properties were systematic studied. The experimental results show that only a relative density about 96.2% of hot-pressing TiB2-30%Al2O3 can be attained due to the plate-like TiB2 particle and its random orientation and excessive Al2O3 grain growth. When sintering temperature is higher than 1 700 ℃, TiB2 grain growth can be found, which obvious improves flexural strength of TiB2 matrix but decreases toughness. It seems that mechanical properties of TiB2-Al2O3 composites are mainly depended on relative density besides grain growth. otherwise, they will be determined by relative density and TiB2 matrix strength together. Anyway, Al2O3 addition can weaken the grain boundary and thus improve the toughness of the materials. A flexural strength of 529 MPa, Vickers hardness of 24.8 GPa and indentation toughness of 4.56 MPa·m1/2 can be achieved inTiB2-30vol% Al2O3.

Phase and microstructure of CVD alumina-silica coating deposited at relative low temperature

Alumina-silica composite coatings were prepared on the surface of graphite paper by CVD using AlCl3/SiCl4/H2/CO2 as precursor in the temperature range of 300 to 550℃. XRD and SEM were used to examine the phase composition and the microstructure of the coating, respectively. The results indicate that the dense, uniform and adherent alumina-silica composite coating can be prepared on graphite paper substrate by CVD at 550℃ using SiCl4/AlCl3/CO2/H2. The alumina-silica composite coating is composed of a number of spherical particles. Each particle is composed of a number of fine-particle. The phase of the 550℃ composite coating includes γ-alumina containing amorphous silica. The content of Cl element in composite coating decreases with the increase of the deposition temperature. The analysis results of morphology and growth mechanisms of the CVD alumina-silica indicate that the condensation within the boundary layer will be more likely to lead to the formation of gel-particles. The gel-particles size decreases with the increase of deposition temperature in the range of 300550℃. Surface reaction is the main path to generate deposition products at 550℃.

Comparative Study on Constitutive Models to Predict Flow Stress of Fe-Cr-Ni Preform Reinforced Al-Si-Cu-Ni-Mg Composite

The isothermal compression tests were carried out on Gleeble-3500 thermal-mechanical simulation machine in a temperature range of 298-473 K and strain rate range of 0.001-10 s^-1. The experimental results show that the flow stress data are negatively correlated with temperature for temperature softening, and the strain rates sensitivity of this composite increases with elevating temperature. Based on the experimental data, Johnson-Cook, modified Johnson-Cook and Arrhenius constitutive models were established. The accuracy of these three constitutive models was analyzed and compared. The results show that the values predicted by Johnson-Cook model could not agree well with the experimental values. The prediction accuracy of Arrhenius model is higher than that of Johnson-Cook model but lower than that of the Modified Johnson-Cook model.

Designing new low alloyed Mg-RE alloys with high strength and ductility via high-speed extrusion

Two new low-alloyed Mg-2RE-0.8Mn-0.6Ca-0.5Zn(wt%,RE=Sm or Y)alloys are developed,which can be produced on an in-dustrial scale via relatively high-speed extrusion.These two alloys are not only comparable to commercial AZ31 alloy in extrudability,but also have superior mechanical properties,especially in terms of yield strength(YS).The excellent extrudability is related to less coarse second-phase particles and high initial melting point of the two as-cast alloys.The high strength-ductility mainly comes from the formation of fine grains,nano-spaced submicron/nano precipitates,and weak texture.Moreover,it is worth noting that the YS of the two alloys can maintain above 160 MPa at elevated temperature of 250°C,significantly higher than that of AZ31 alloy(YS:45 MPa).The Zn/Ca solute segregation at grain boundaries,the improved heat resistance of matrix due to addition of RE,and the high melting points of strengthening particles(Mn,MgZn_(2),and Mg-Zn-RE/Mg-Zn-RE-Ca)are mainly responsible for the excellent high-temperature strength.

Toward the development of Mg alloys with simultaneously improved strength and ductility by refining grain size via the deformation process

Magnesium(Mg) alloys, as the lightest metal engineering materials, have broad application prospects.However, the strength and ductility of traditional Mg alloys are still relativity low and difficult to improve simultaneously.Refining grain size via the deformation process based on the grain boundary strengthening and the transition of deformation mechanisms is one of the feasible strategies to prepare Mg alloys with high strength and high ductility.In this review, the effects of grain size on the strength and ductility of Mg alloys are summarized, and fine-grained Mg alloys with high strength and high ductility developed by various severe plastic deformation technologies and improved traditional deformation technologies are introduced.Although some achievements have been made, the effects of grain size on various Mg alloys are rarely discussed systematically and some key mechanisms are unclear or lack direct microscopic evidence.This review can be used as a reference for further development of high-performance fine-grained Mg alloys.

A prospective randomized trial of transnasal ileus tube vs nasogastric tube for adhesive small bowel obstruction

AIM:To study the therapeutic efficacy of a new transnasal ileus tube advanced endoscopically for adhesive small bowel obstruction.METHODS:A total of 186 patients with adhesive small bowel obstruction treated from September 2007 to February 2011 were enrolled into this prospective randomized controlled study.The endoscopically advanced new ileus tube was used for gastrointestinal decompression in 96 patients and ordinary nasogastric tube(NGT) was used in 90 patients.The therapeutic efficacy was compared between the two groups.RESULTS:Compared with the NGT group,the ileus tube group experienced significantly shorter time for relief of clinical symptoms and improvement in the findings of abdominal radiograph(4.1 ± 2.3 d vs 8.5 ± 5.0 d) and laboratory tests(P < 0.01).The overall effectiveness rate was up to 89.6% in the ileus tube group and 46.7% in the NGT group(P < 0.01).And 10.4% of the patients in the ileus tube group and 53.3% of the NGT group underwent surgery.For recurrent adhesive bowel obstruction,ileus tube was also significantly more effective than NGT(95.8% vs 31.6%).In the ileus tube group,the drainage output on the first day and the length of hospital stay were significantly different depending on the treatment success or failure(P < 0.05).The abdominal radiographic improvement was correlated with whether or not the patient underwent surgery.CONCLUSION:Ileus tube can be used for adhesive small bowel obstruction.Endoscopic placement of the ileus tube is convenient and worthy to be promoted despite the potential risks.

Experimental Investigation on Microstructure and Segregation of Ultrahigh Strength Al-Zn-Mg-Cu-Zr-Sc-Ni Alloy during Homogenization

Ultrahigh strength Al-12Zn-2.4Mg-1.1Cu-0.20Zr-0.30Sc-0.30Ni alloy billets were fabricated by spray deposition method(the Osprey process). The effect of homogenization treatment on the microstructures and tensile properties were investigated by OM, SEM and EDS. The results show that adding small amount of Sc and Zr can greatly refine the grain size of the billet, with the average grain size of 10 μm. Grain-boundary becomes coarser firstly and then thinner under different homogenizing condition and grain coarsening were observed. The solute elements content of Zn inside grains has a peak at 490 ℃ /2 h, and Cu element, which was solved into matrix, can enhance the matrix hardness obviously during homogenization. The suitable homogenizing treatment is 460～490 °C/2 h for the hot extrusion of the studied alloy; after the optimized solid solution and T6 aging, the highest ultimate tensile strength (UTS) is 858 MPa with a ductility of 4.8%.

Development of Evaluation Technique of GMAW Welding Quality Based on Statistical Analysis

Nondestructive techniques for appraising gas metal arc welding（GMAW） faults plays a very important role in on-line quality controllability and prediction of the GMAW process. On-line welding quality controllability and prediction have several disadvantages such as high cost, low efficiency, complication and greatly being affected by the environment. An enhanced, efficient evaluation technique for evaluating welding faults based on Mahalanobis distance（MD） and normal distribution is presented. In addition, a new piece of equipment, designated the weld quality tester（WQT）, is developed based on the proposed evaluation technique. MD is superior to other multidimensional distances such as Euclidean distance because the covariance matrix used for calculating MD takes into account correlations in the data and scaling. The values of MD obtained from welding current and arc voltage are assumed to follow a normal distribution. The normal distribution has two parameters： the meanm and standard deviations of the data. In the proposed evaluation technique used by the WQT, values of MD located in the range from zero tom＋3s are regarded as “good”. Two experiments which involve changing the flow of shielding gas and smearing paint on the surface of the substrate are conducted in order to verify the sensitivity of the proposed evaluation technique and the feasibility of using WQT. The experimental results demonstrate the usefulness of the WQT for evaluating welding quality. The proposed technique can be applied to implement the on-line welding quality controllability and prediction, which is of great importance to design some novel equipment for weld quality detection.

Influence of isochronal heat treatment on damping behavior of AZ61 alloy

Strain amplitude dependence of the logarithmic decrement was measured and studied on an AZ61 magnesium alloy at room temperature. Measurements were carried out before and after isochronal thermal treatment step by step with increasing temperature. For all specimens, the strain dependence of the logarithmic decrement exhibits two regions. At lower strains the logarithmic decrement is strain independent and in the higher strain region it depends strongly on strain amplitude. The strain-independent logarithmic decrement is mainly composed of thermoelastic damping and dislocation damping, which can be explained by Granato-Lticke theory. In addition, the strain-independent logarithmic decrement for the specimens annealed at higher temperatures is a little lower than that for as-cast specimen, and it increases with increasing temperature of heat treatment. Microstructure changes due to heat treatment are responsible for changes of the logarithmic decrement.

Preparation of FVS1212/FVS0812 materials and its mechanical properties

FVS1212/FVS0812 material was prepared by adding FVS1212 powder into FVS0812 powder. The structure and mechanical properties of materials were studied by means of X-Ray, tensile measurement, OM and SEM. The results show that adding proper content FVS1212 powders can improve the tensile strength of FVS0812 aluminum at room temperature and elevated temperature, and that the elongation of FVS1212/FVS0812 material is better than that of FVS1212 aluminum.

进浇方式对平面PP注塑件表面颜色和光泽的影响

研究了不同进浇方式对车内可视区域平面聚丙烯(PP)注塑产品表面颜色和光泽的影响。结果表明,在相同注塑工艺下,侧面两点进浇方式的产品,左右两侧的L值差异最小,最大差值仅为0.1,并且,左右两侧光泽度一致,色泽一致性得到了明显改善。通过模流分析发现,相比于单点和三点进浇方式,在两点进浇方式下,注塑过程中产品左右两侧的V/p转换压力和温度差异最小。并且,有利于产品表面皮纹深度的均匀性,改善色差问题。此外,随着V/p转换压力和熔体温度的升高,材料的流动性逐渐升高,产品对皮纹的复制能力逐渐提高,从而使距离浇口位置越近的区域表面光泽度越低,L值越高。

The Heat Treatment Behavior of Super-High Strength Aluminum Alloys by Spray Forming

In order to understand the stress corrosion behavior of super-high strength aluminum alloys by spray forming, different aluminum alloys by different heat treatment was made. The results showed that the alloy with peak aging has the most sensitive stress corrosion cracking, the crack can even be seen using eyes;the alloys with two step aging were better than one step aging alloys, the alloys has not been found stress corrosion cracking.

Mechanical properties,corrosion behavior and microstructure evolution of zinc and scandium co-strengthened 5xxx alloy

Nowadays,it is a challenge to improve the strength of 5xxx aluminium alloy while maintaining its distinctive properties.To address this,the Zn and Sc modified high strength 5xxx aluminium alloys with good intergranular corrosion resistance were prepared through chill casting,and the effects of minor Sc on mechanical properties,corrosion behavior and microstructure evolution of Al-5.0Mg-3.0Zn alloys were systematically investigated.The results show that the Sc containing alloy has high number density and small size of intragranular precipitates,combined with the solid solution strengthening of Sc and the Al_(3)(Sc_(1-x),Zr_(x))second phase strengthening,the strength of Al-5.0Mg-3.0Zn-0.1Sc alloy is obviously enhanced.Meanwhile,the intergranular corrosion resistance of the Sc containing alloy is also improved due to the formation of a large number of low angle grain boundaries and the weakening of the continuity of precipitated phases along the grain boundaries.

Simultaneously improving mechanical and anti-corrosion properties of extruded Mg-Al dilute alloy via trace Er addition

Simultaneously improving the mechanical properties and corrosion resistance of magnesium(Mg)alloys is a long-standing challenge to be solved in their engineering applications.In this work,we find that trace Er addition can improve the mechanical and anti-corrosion properties of Mg-1.4Al-0.4Mn-0.4Ca-0.3Er(wt%,AMXE)dilute alloy synergistically,especially reducing the corrosion rate(0.75 mm y-1)by one order of magnitude compared with the reference Mg-1.4Al-0.4Mn-0.4Ca(AMX)alloy and making it comparable to that of high-purity Mg.Adding trace Er reduces the dynamic recrystallization degree and increases the strengthening phase particles,which is mainly responsible for the increase of yield strength by 42 MPa.The addition of Er promotes the formation of much less noble Al8Mn4Er with effective Fe trapping ability and induces dislocation segregation,thus dramatically reducing micro-galvanic corrosion tendency.Meanwhile,Er addition promotes the formation of a more passivation and dense corrosion film.These two factors together lead to the extremely low corrosion rate of AMXE alloy.Our findings are expected to promote the development of low alloyed high performance Mg alloys.