钇对Mg-9Al-1Si合金蠕变抗力和微观组织的影响

研究了Mg-9Al-1Si-xY合金的高温蠕变性能及其微观组织与力学性能的关系。该合金中的主要强化相Mg2Si呈粗大的汉字状，分布在晶界的周围，在受到应力时，这种汉字状相与基体的界面处易产生微裂纹，降低合金的抗拉强度、塑性等力学性能。在Mg-9Al-1Si合金中加入微量的Y以后，合金的组织得到明显的细化，Mg2Si强化相形貌由粗大的汉字状转变为细小、弥散分布的颗粒状。显微组织的改善，使得Mg-9Al-1Si合金的室温和高温力学性能均有一定的提高，并明显改善了Mg-9Al-1Si的抗蠕变性能。     

钕对Mg7Zn2Al镁合金显微组织及力学性能的影响

采用光学显微镜、XRD、SEM和万能实验机等手段研究了稀土Nd(0.3%,0.6%,0.9%)对Mg7Zn2Al镁合金显微组织和力学性能的影响。结果表明:Mg7Zn2Al镁合金中添加Nd后,显微组织中有针状或棒状的Al2Nd和AlNd等稀土相生成,合金中的共晶组织(α-Mg+Mg32(Al,Zn)49+Mg7Zn3)得到了明显细化;但是α-Mg有粗化趋势,呈现发达的树枝状或胞状,共晶相由粗大连续的网状变为细小的块状或颗粒状分布在树枝晶的一次枝晶臂或二次枝晶臂的间隙。随着Nd含量的增加,合金的抗拉强度和延伸率呈逐渐下降趋势,显微组织的粗化是造成合金拉伸性能降低的主要原因,而硬度没有明显的变化。     

铒和钕对铸态ZK60镁合金显微组织和力学性能的影响

研究了铒和钕对铸态ZK60镁合金显微组织和力学性能的影响。结果表明：ZK60镁合金中添加Er或Nd能够细化晶粒，改变合金的显微组织。当ZK60镁合金中加入1．0％（质量分数）的Er或Nd具有最佳的细化效果，与原ZK60镁合金晶粒尺寸相比较，晶粒的平均直径由原来的33．0μm分别减少至23．6和25．2μm。添加Er或Nd的ZK60镁合金形成古有Er或Nd的稀土共晶相，其熔点为518℃。稀土共晶相对晶粒具有钉扎作用，提高合金在150℃时的抗拉强度。稀土共晶相的形态和分布对室温力学性能有显著影响。含有Er的共晶相析出数量较少，沿晶界不连续分布，提高合盒室温强度的同时塑性略有改善，而含有Nd的共晶相形态粗大，析出数量较多，沿晶界网状连续分布，合金固溶强化效果明显减弱，室温强度和塑性均降低。     

Mg-SiO_2体系制备Mg_2Si/AZ91D复合材料的研究

采用原位合成技术制备了Mg2Si/AZ91D复合材料,并通过光学显微镜(OM)、扫描电镜(SEM)、能谱仪(EDS)和X射线衍射仪(XRD)等对添加碱土、稀土元素的影响进行了研究。结果表明:AZ91D镁合金中加入SiO2(其中Si占合金质量的3%)后,出现多边形状或树枝晶状的初生Mg2Si相,以及汉字状的共晶Mg2Si相,树枝晶状Mg2Si的平均尺寸约25~50μm,汉字状Mg2Si的平均尺寸约12~15μm;Mg2Si对镁合金中的β-Mg17Al12相有细化作用。添加Ca,Sr,Y对Mg2Si形貌、尺寸有明显的改善,当添加0.9%Ca,0.1%Sr,0.5%RE(80%Y)变质处理后,Mg2Si形貌全部变为多边形状,平均尺寸约0.8~5μm。     

锌对稀土镁合金组织与力学性能的影响

采用OM, XRD, SEM和EDS等试验手段研究了Zn对稀土镁合金Mg-4Y-1Ca(%,质量分数)微观组织和力学性能的影响。结果表明:随着Zn (x=1%, 3%, 5%)的加入, Mg-4Y-1Ca合金中生成的Mg_(24)Y_5二元相逐步转变为Mg_3Y_2Zn_3(W相)+Mg_(12)YZn(X相)三元相,铸态组织细化,第二相沿晶界成网状分布;经热挤压变形后,合金再结晶后晶粒细化明显,第二相弥散分布于基体和晶界上,强度提高的同时伸长率也获得较大提升,其中Mg-4Y-1Ca-5Zn合金表现最为显著。得益于Zn添加对再结晶晶粒细化和W相、 X相弥散强化的共同作用, Mg-4Y-1Ca-5Zn合金经热挤压处理后具有较佳的综合力学性能,屈服强度、抗拉强度和伸长率分别达到198 MPa, 271 MPa和24.6%。     

Mg-13Gd-2Nd-2Cu合金的显微组织与力学性能

通过熔炼铸造及热挤压方法制备了Mg-13Gd-2Nd-2Cu(质量分数)镁合金。通过金相显微镜、扫描电镜及能谱分析、维氏硬度、拉伸性能测试等方法,研究了Mg-13Gd-2Nd-2Cu合金的铸态显微组织特征及退火温度对挤压态合金的组织与力学性能影响。结果表明:退火热处理促进了晶界处Mg5(GdNdCu)_1相充分溶入α-Mg基体中。提高退火温度使基体晶粒发生再结晶长大,改变了Mg5(GdNdCu)_1相的形态和分布。当退火温度超过500℃时,晶粒粗化并部分发生过烧现象。提高退火温度,会使挤压态合金的屈服强度有所降低。     

镧对Mg-Si合金中Mg2Si相变质的影响

研究了Mg-5Si合金中La的添加对初生Mg2Si相变质的影响。结果表明,适量的La能够有效地变质初生Mg2Si相。基于本文的研究,在添加约0.5%La时,获得了最佳的变质效果,此时,初生Mg2Si相的尺寸减小到25μm以下,其形态从粗大的树枝形状变为多面体形状。然而,当La增加到0.8%或者更高时,初生Mg2Si相又生长为粗大的树枝形态。而且,在凝固过程中发现形成了一些LaSi2化合物,这些化合物的数量随着La的增加而呈现逐渐增加的趋势。     

镱对AZ91D镁合金显微组织和力学性能的影响

在Mg-9Al-1Zn合金的基础上添加不同质量分数的Yb, 制备了4种合金. 通过X射线衍射、金相显微镜、扫描电镜及能谱分析仪等手段分析了Yb的添加对AZ91D显微组织和力学性能的影响. 结果表明: Yb的加入, 显著改变了AZ91D合金的铸态组织, 细化了β-Mg17Al12相, 且β-Mg17Al12脆性相由连续网状分布逐渐变为离散状, 同时晶界上出现了块状的Al11Yb3和点状Al6Mn4Yb化合物. 当Yb含量为1.0%时, 该合金具有最佳的综合力学性能, 抗拉强度达到194 MPa, 比AZ91D提高22%, 伸长率和硬度也随着Yb含量的增加而提高. 研究表明, 重稀土元素Yb在镁合金中显示出与轻稀土更相近的作用效果.     

含钪Al-Zn-Mg-Cu-Zr合金组织性能的研究

采用金相显微镜、扫描电子显微镜和透射电子显微镜研究了微量钪对Al-Zn-Mg-Cu-Zr系合金组织的影响，测试了不同热处理状态下台金的力学性能和电导率。结果表明，添加微量Sc可以明显细化合金的铸态晶粒，显著提高Al-Zn-Mg-Cu-Zr合金的力学性能和电导率，其作用机制主要为AJ3（Sc，Zr）引起的细晶强化、亚结构强化和沉淀强化；Al-9．0Zn-2．5Mg-1．2Cu-0．15Zr-0．12Sc和Al-9．5Zn-2．5Mg-1．2Cu-0．15Zr-0．12Sc经强化固溶和T6处理后，抗拉强度分别达到829．4和818．6MPa。     

钇对Mg-5Zn-2Al合金组织和力学性能的影响

利用金相显微镜、电子万能试验机、扫描电镜和X射线等手段,研究了不同含量的Y对Mg-5Zn-2Al镁合金铸态及热处理状态下组织及力学性能的影响.结果表明:合金主要由α-Mg基体相、Mg32(Al,Zn)49相及Al3Y相组成,并且A13Y稀土相随着合金中加Y量的增加而增多.在铸态及热处理条件下,合金的力学性能(抗拉强度和延伸率)均呈现先下降后上升的变化趋势.在铸态条件下,当加Y量为0.3%时合金的抗拉强度达到最大,为205 MPao当加Y量为0.9%时,合金的延伸率达到最大,为14.6%.经过T6热处理后,合金的抗拉强度较铸态均得到了明显提高,而延伸率有所下降.加Y量为0.9%的Mg-5Zn-2Al镁合金的抗拉强度和延伸率均达到最大值,分别为234 MPa和11.4%.     

Microstructural and Mechanical Properties of Al-20%Si Containing Cerium

In this paper the effect of cerium addition in hypereutectic Al-Si alloys was studied. Casting method was used to produce Al-20Si with variation of Ce contents. The sample characterization studied was investigated by Optical Microscope, X-ray fluorescence and X-ray Diffraction. Vickers microhardness and wear test was carried out to study the influence of Ce towards the Al-20Si alloys. The addition of Ce in the Al-20Si alloys refined the Si primary phase as the Ce content increases. The results showed that the addition of 0.46 to 2.24 wt.% of cerium in Al-20Si alloys led to the formation of fine cells dispersed in the Al-matrix. These fine cells consist of a mixture of eutectic Si particles and intermetallic Al3Ce and CeAl1.2Si0.8 phase in Al matrix. The amount of rod- like intermetallic Al3Ce and CeAl1.2Si0.8 phase increases with increasing Ce content. The microhardness of Al-20Si alloys increases with the increase in Ce content. Addition of Ce up to 1.61 wt.% Ce improve the wear properties of Al-20Si alloy.     

Investigations of the distribution of elements in phases present in G-AlMg5Si cast alloy with EDX/WDX spectrometers and AES

The mechanical properties of most aluminium alloys depend heavily on chemical composition, casting methods and heat treatment. Alloys of type G-AlMg₅Si are known for good corrosion resistance and mechanical properties at elevated temperatures. Under the designation Hydronalium (Hy 511) they are used for the production of heads for air cooled Diesel engines. To obtain better mechanical characteristics, titanium is added to the alloy. This paper deals with the results obtained during investigations of the distribution of elements in binary eutectic Mg₂Si and ternary eutectic as well as the distribution of titanium in samples of Hy 511, obtained during casting of cylinder heads. Studies of the distribution of the elements were performed using EDX/ WDX spectrometry, and the distribution of titanium was studied also with Auger electron spectroscopy.Dedicated to Professor Günther Tölg on the occasion of his 60th birthday     

Effect of Molybdenum (Mo) Addition on Phase Composition,Microstructure, and Mechanical Properties of Pre-Alloyed Ti6Al4V Using Spark Plasma Sintering Technique

The effect of molybdenum additions on the phases, microstructures, and mechanical properties of pre-alloyed Ti6Al4V was studied through the spark plasma sintering technique. Ti6Al4V-xMo (where x = 0, 2, 4, 6 wt.% of Mo) alloys were developed, and the sintered compacts were characterized in terms of their phase composition, microstructure, and mechanical properties. The results show that the equiaxed primary alpha and Widmänstatten (alpha + beta) microstructure in pre-alloyed Ti6Al4V is transformed into a duplex and globular model with the increasing content of Mo from 0 to 6%. The changing pattern of the microstructure of the sample strongly influences the properties of the material. The solid solution hardening element such as Mo enhances mechanical properties such as yield strength, ultimate tensile strength, ductility, and hardness compared with the pre-alloyed Ti6Al4V alloy.     

The effects of a eutectic modifier on microstructure and surface corrosion behavior of Al-Si hypoeutectic alloys

Hypoeutectic aluminum–silicon alloys can have significant improvements in mechanical properties by inducing structural modification in the normally occurring eutectic. The eutectic modification may affect not only the mechanical properties but also the corrosion resistance of such alloys. It is well known that structural parameters such as grain size and interdendritic spacing can significantly affect corrosion resistance of alloys. However, to date, few researches have been performed to experimentally evaluate the effects of an effective modification of eutectic morphology on surface corrosion behavior of Al–Si alloys. In the present study, modified and unmodified samples of an Al 9 wt.% Si alloy were solidified under similar solidification conditions, and after metallographic procedures, the corrosion resistance was analyzed by both the electrochemical impedance spectroscopy technique and the Tafel extrapolation method carried out in a 0.5 M NaCl test solution at 25 °C. The impedance parameters and corrosion rate were obtained from an equivalent circuit analysis. It was found that the Al-9 wt.% Si alloy casting in the modified condition tends to have its corrosion resistance decreased when compared to the unmodified alloy.     

Photocatalytic,phosphorus-doped,anatase oxide layers applicable to titanium implant alloys

Titanium alloys provide excellent corrosion resistance and favorable mechanical properties well suited for a variety of biomaterial applications. The native oxide surface on titanium alloys has been shown to be less than ideal and surface modification is often needed. Previously, an optimized anodization process was shown to form a porous phosphorus-enhanced anatase oxide layer on commercially pure Ti grade 4. The anodized layer was shown to improve osseointegration and to reduce bacteria attachment when photocatalytically activated with UVA preillumination. The primary objective of the present study was to create a similar phosphorus-enhanced anatase oxide layer on series of titanium alloys including commercially pure Ti grade 4, Ti-6Al-7Nb, Ti-6Al-4V ELI, alpha + beta Ti-15Mo, beta Ti-15Mo, and Ti-35Nb-7Zr-5Ta. Phosphorus-enhanced anatase oxide layers were formed on each titanium substrate. Anatase formation was shown to generally increase with oxide thickness, except on substrate alloys containing niobium. Phosphorus uptake was shown to be dependent on the titanium alloy chemistry or microstructure. Anodized layers formed on beta-structured titanium alloys revealed the lowest phosphorus uptake and the most nanosized surface porosity. A methylene blue degradation assay showed anodized layers on commercially pure Ti and both Ti-15Mo alloys to exhibit the highest levels of photocatalytic activity. Given the range of mechanical properties available with the commercially pure Ti and Ti-15Mo alloys, the results of this study indicate the benefits of phosphorus-enhanced anatase oxide coatings may be applicable to a wide variety of biomaterial applications.     

Effects of Ca and Ag addition and heat treatment on the corrosion behavior of Mg-7Sn alloys in 3.5 wt.% NaCl solution

The effects of 1 wt.% Ca or 1 wt.% Ca + 1 wt.% Ag addition and heat treatment on the corrosion behavior of Mg-7Sn (wt.%) alloy in 3.5 wt.% NaCl solution were investigated by electrochemical measurements and immersion tests. The alloys were characterized by optical microscope (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). It was found that all alloys were corroded by pitting corrosion and grain boundary corrosion and further corroded with time going. Loose layers of compounds, including Mg (OH)₂, MgO, SnO₂, and other compounds containing Ca and Ag elements, were calibrated on the surface of corroded Mg-7Sn-1Ca-1Ag alloy. The Ca addition improved the corrosion resistance of Mg-7Sn alloy due to the formation of relatively stable compounds containing calcium element and grains refinement. Furthermore, the solid solutioned alloys obtained a superior corrosion resistance due to the dissolve of eutectic Mg₂Sn phase and homogenization treatment. However, the aging treatment is slightly detrimental to the corrosion resistance of Mg-7Sn alloys with the formation of Mg₂Sn precipitates. In conclusion, the aged Mg-7Sn-1Ca-1Ag alloy exhibited a better corrosion resistance and a noticeable micro-hardness property compared with those of as-cast Mg-7Sn alloy. And this study provides an important idea for the research on the comprehensive properties of Mg-Sn alloys.