Effect of minor Sc on the microstructure and mechanical properties of AZ91 Magnesium Alloy

The as-cast and heat-treated microstructures and mechanical properties of the AZ91 magnesium alloys with and without minor Sc addition were investigated and compared in this paper. The results indicated that adding0.15–0.45 wt% Sc to the as-cast AZ91 alloy not only could modify and refine the Mg_(17)Al_(12) phase but also suppress the formation of the Mg_(17)Al_(12) phase. At the same time, the grains of the Sc-containing as-cast AZ91 alloys were also effectively refined. As a result, the mechanical properties at room temperature(RT) for the Sccontaining as-cast AZ91 alloys were effectively improved. In addition, adding 0.15–0.45 wt%Sc to the AZ91 alloy promoted the formation of the continuous precipitates(CP) during the aging treatment in spite of that the formation of the discontinuous precipitates(DP) was simultaneously suppressed. Accordingly, the Sc-containing as-aged AZ91 alloys obtained the relatively higher mechanical properties at RT than the as-aged AZ91 alloy.     

Analysis of EET on Ca increasing the melting point of Mg17Al12 phase

The present investigation showed that the additions of Ca to the alloy AZ91 were mainly dissolved into the Mg₁₇Al₁₂ phase and increased its melting point and thermal stability, which would have great effects on the high-temperature properties of AZ91 alloy. The empirical electron theory (EET) of solid and molecules was used to calculate the valence electron structures (VES) of Mg₁₇Al₁₂ intermetallic compound with and without Ca addition. The results showed that Ca dissolving in Mg₁₇Al₁₂ phase increased the strength of bonds that control the thermal stability of Mg₁₇Al₁₂ phase. Additions of Ca also made the distribution of the valence electrons on the dominant bond network more uniform in the whole unit cell of Mg₁₇Al₁₂. The theoretical conclusions well account for the experimental results.     

Formation mechanism of an aluminium-based chemical conversion coating on AZ91D magnesium alloy

An environmentally clean aluminium-based conversion coating on AZ91D magnesium alloy was studied in aluminium nitrate solutions. The morphology, composition, structure, and formation mechanism of the coating were investigated in detail using scanning electron microscopy/energy dispersion spectrometry, X-ray diffraction, transmission electron microscopy, and electrochemical corrosion tests. The results show that the conversion coating is composed of magnesium, aluminium, and oxygen, and shows an amorphous structure. In the initial stage of coating formation, the grain-like nucleus is composed of Al₁₀O₁₅·xH₂O, (Al₂O₃)_5.333, Al₂O₃, AlO(OH), MgAl₂O₄, (Mg_0.88Al_0.12)(Al_0.94Mg_0.06)₂O₄, and (Mg_0.68Al_0.32)(Al_0.84Mg_0.16)₂O₄. The conversion coating formed in the 0.01 mol/L aluminium nitrate solution for 15 min can improve the corrosion resistance of the magnesium alloy greatly. The discussion reveals that the possible formation mechanism for the aluminium-based conversion coating is the reduction reaction on micro-cathodic sites due to the electrochemically heterogeneous magnesium alloy substrate.     

Effects of P addition on the microstructure and mechanical properties of Mg–5%Sn–1.25%Si alloy

The effects of Al-P addition on the microstructure and mechanical properties of as-cast Mg–5%Sn–1.25%Si magnesium alloy were investigated. The results show that the phases of the as-cast alloy are composed of α-Mg, Mg2 Sn, Mg2 Si, little P, and AlP. The Chinese character shape Mg2 Si phase changes into a granular morphology by P addition because AlP can act as a heterogeneous nucleation core for the Mg2 Si phase. When 0.225wt% of Al–3.5%P alloy is added, the mechanical properties of the Mg–5%Sn–1.25%Si alloy are greatly improved, and the tensile strength increases from 156 to 191 MPa, an increase of 22.4% compared to the alloy without P addition. When the amount of Al–3.5%P reaches 0.300wt%, a segregation phenomenon occurs in the granular Mg2 Si phase, and the tensile strength and hardness decrease though the elongation increases.     

Corrosion behavior of as-cast Mg–8Li–3Al+xCe alloy in 3.5wt% NaCl solution

Mg–8Li–3Al+xCe alloys (x = 0.5wt%, 1.0wt%, and 1.5wt%) were prepared through a casting route in an electric resistance furnace under a controlled atmosphere. The cast alloys were characterized by X-ray diffraction, optical microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The corrosion behavior of the as-cast Mg–8Li–3Al+xCe alloys were studied under salt spray tests in 3.5wt% NaCl solution at 35°C, in accordance with standard ASTM B–117, in conjunction with potentiodynamic polarization (PDP) tests. The results show that the addition of Ce to Mg–8Li–3Al (LA83) alloy results in the formation of Al₂Ce intermetallic phase, refines both the α-Mg phase and the Mg₁₇Al₁₂ intermetallic phase, and then increases the microhardness of the alloys. The results of PDP and salt spray tests reveal that an increase in Ce content to 1.5wt% decreases the corrosion rate. The best corrosion resistance is observed for the LA83 alloy sample with 1.0wt% Ce.     

Mechanical and wear properties of Al-Al3Mg2 nanocomposites prepared by mechanical milling and hot pressing

β-Al₃Mg₂ intermetallic was used as a reinforcing agent to improve the mechanical properties of an aluminum matrix. Different amounts of Al₃Mg₂ nanoparticles (ranging from 0wt% to 20wt%) were milled with aluminum powders in a planetary ball mill for 10 h. Consolidation was conducted by uniaxial pressing at 400°C under a pressure of 600 MPa for 2 h. Microstructural characterization confirms the uniform distribution of Al₃Mg₂ nanoparticles within the matrix. The effects of nano-sized Al₃Mg₂ content on the wear and mechanical properties of the composites were also investigated. The results show that as the Al₃Mg₂ content increases to higher levels, the hardness, compressive strength, and wear resistance of the nanocomposites increase significantly, whereas the relative density and ductility decrease. Scanning electron microscopy (SEM) analysis of worn surfaces reveals that a transition in wear mechanisms occurs from delamination to abrasive wear by the addition of Al₃Mg₂ nanoparticles to the matrix.     

Two distinct roles of Al2Sm and Al11Sm3 phases on the corrosion behavior of the magnesium alloy Mg-5Sm-xAl

The roles of Al₁₁Sm₃ and Al₂Sm phases on microstructure evolution, mechanical properties and corrosion behavior of the Mg-5Sm-xAl system was investigated. The results showed that adding Al to Mg–5Sm binary alloy brought two Al–Sm phases, Al₁₁Sm₃ and Al₂Sm, which had two distinct roles regarding the microstructure evolution, mechanical properties and corrosion behavior of the Mg-Sm-Al alloy. Al₁₁Sm₃ produced a strong galvanic couple with the Mg matrix, and significantly accelerated the corrosion. The Al₂Sm particles promoted heterogeneous nucleation and refined the grains, which increased the tensile strength and ductility. Both types of Al–Sm particles provided strengthening effect for the alloy. With higher Al contents, Al₂Sm formed an Al oxide protective surface layer and increased corrosion resistance.     

A bulk metal/ceramic composite material with a cellular structure

Metal/ceramic composite materials can be divided into two groups: one is ceramic reinforced metal matrix composite, and the other is metal toughened ceramic matrix composite. The research on these materials mainly focuses on the mechanical properties due …     

Effects of Sb and heat treatment on the microstructure of Al-15.5wt%Mg2Si alloy

The modification effects of alloying element Sb and heat treatment on Al-15.5wt%Mg₂Si alloy were investigated by Olympus microscopy (OM), scanning electron microscopy and energy disperse spectroscopy (SEM-EDS), and X-ray diffraction (XRD). It is found that Sb plays a significant role in shaping primary Mg₂Si phase and eutectic Mg₂Si phase in Al-15.5wt%Mg₂Si alloy. The Sb addition of about 1.0wt% makes the resultant alloy show the finest primary Mg₂Si phase and the eutectic Mg₂Si phase with well distribution. But further increasing the Sb content decreases the amount of primary Mg₂Si phase, and some segregated phases appear at regions between the grains. In addition, heat treatment can modify the microstructural feature of Sb-modified Al-15.5wt%Mg₂Si alloy in terms of obviously shortening the nodulizing time of primary Mg₂Si phase and eutectic Mg₂Si phase.     

Effects of gadolinium addition on the microstructure and mechanical properties of Mg-9Al alloy

This research aims to study the significance of Gd addition (0wt%-2wt%) on the microstructure and mechanical properties of Mg-9Al alloy. The effect of Gd addition on the microstructure was investigated via X-ray diffraction (XRD), optical microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The Mg-9Al alloy contained two phases, α-Mg and β-Mg17Al12. Alloying with Gd led to the emergence of a new rectangular-shaped phase, Al₂Gd. The grain size also decreased marginally upon Gd addition. The ultimate tensile strength and microhardness of Mg-9Al alloy increased by 23% and 19%, respectively, upon 1.5wt% Gd addition. We observed that, although Mg-9Al-2.0Gd alloy exhibited the smallest grain size (181 μm) and the highest dislocation density (5.1×1010 m-2) among the investigated compositions, the Mg-9Al-1.5Gd alloy displayed the best mechanical properties. This anomalous behavior was observed because the Al₂Gd phase was uniformly distributed and present in abundance in Mg-9Al-1.5Gd alloy, whereas it was coarsened and asymmetrically conglomerated in Mg-9Al-2.0Gd.     

CaCO3在AZ31镁合金中的细化效果及机理

用CaCO3作细化剂研究了对AZ31镁合金凝固组织的影响.结果表明:在AZ31中添加质量分数为0.5%的CaCO3,在760℃保温10 min后细化效果最佳,α-Mg晶粒的尺寸由基体合金的570μm降至209μm,降幅约63.3%.通过能谱分析、结合能和自由能的计算证实,细化机理是CaCO3反应后生成Al4C3,其中部分Al4C3质点作为异质核心,使晶粒细化,其余的Al4C3质点钉扎晶界也阻碍了晶粒长大.Al元素随固/液界面前沿被快速推至晶界,生成沿晶界生长的β-Mg17Al12相,起到进一步固定晶界的作用.合金元素的分布均有改变.     

Mn-ion-enhanced red spectral emission from yttrium aluminum garnet doped cerium phosphor

Mnions were co-doped in yttrium aluminum garnet doped cerium(YAG:Ce) phosphors as a co-activator and host lattice element using the co-precipitation method.These ions broadened the emission spectra of the pure YAG:Ce phosphor,which is caused by the 2E-4A2,5E-5T2 or 1T2-5T2 transition.From our X-ray diffraction results,we observed that Ce3+(1.032 ) was substituted at the Y3+(0.900 ) site,and Mn4+(0.538 ) and Mn3+(0.67 ) were substituted at the Al3+(0.535 ) site.The chromaticity color co-ordinates of YAG:Ce0.06 is(0.203,0.167),and the indices of YAG:Ce0.06,Mn0.04 and YAG:Ce0.06,Mn0.08 are(0.249,0.181) and(0.233,0.194),respectively.The manganese co-doped yttrium aluminum garnet doped cerium blended with the YAG:Ce phosphor showed improved white light emission.     

Microstructure evolution and mechanical properties of a large-sized ingot of Mg-9Gd-3Y-1.5Zn-0.5Zr (wt%) alloy after a lower-temperature homogenization treatment

In this paper, a large-sized ingot of Mg-9Gd-3Y-1.5Zn-0.5Zr (wt%) alloy with a diameter of 600 mm was successfully prepared by the semi-continuous casting method. The alloy was subsequently annealed at a relatively low temperature of 430℃ for 12 h as a homogenization treatment. The microstructure and room-temperature mechanical properties of the alloy were investigated systematically. The results show that the as-cast alloy contained a mass of discontinuous lamellar-shaped 18R long-period stacking ordered (LPSO) phases with a composition of Mg₁₀ZnY and an α-Mg matrix, along with net-shaped Mg₅(Y,Gd) eutectic compounds at the grain boundaries. Most of the eutectic compounds dissolved after the homogenization treatment. Moreover, the amount and dimensions of the lamellar-shaped LPSO phase obviously increased after the homogenization treatment. The structure of the phase transformed into 14H-type LPSO with composition Mg₁₂Zn(Y,Gd). The mechanical properties of the heat-treated large-sized alloy ingot are uniform. The ultimate tensile strength (UTS) and tensile yield strength (TYS) of the alloy reached 207.2 MPa and 134.8 MPa, respectively, and the elongation was 3.4%. The high performances of the large-sized alloy ingot after the homogenization treatment is attributed to the strengthening of the α-Mg solid solution and to the plentiful LPSO phase distributed over the α-Mg matrix.     

白光LED用橙色发射荧光粉Y_3Mg_2AlSi_2O_(12)∶Ce~(3+)的制备研究

采用X射线衍射(XRD)、扫描电子显微镜(SEM)、激发-发射光谱及反射光谱等手段,研究了以尿素为燃料的溶胶-凝胶燃烧法,制备白光LED用Y_3Mg_2AlSi_2O_(12)∶Ce~(3+)荧光粉过程中的还原温度、Ce~(3+)浓度等因素,对荧光粉结构、形貌和发光性能的影响.比较了溶胶-凝胶燃烧法和高温固相反应法制备的Y_3Mg_2AlSi_2O_(12)∶Ce~(3+)荧光粉的结晶度、形貌和发光性能,并从反应过程对造成两者差异的原因进行了讨论.     

High thermal conductivity and high strength magnesium alloy for high pressure die casting ultrathin-walled components

With the rapid development of 3C industries,the demand for high-thermal-conductivity magnesium alloys with high mechanical performance is increasing quickly.However,the thermal conductivities of most common Mg foundry alloys(such as Mg-9wt%-1wt%Zn)are still relatively low.In this study,we developed a high-thermal-conductivity Mg-4Al-4Zn-4RE-1Ca(wt%,AZEX4441)alloy with good mechanical properties for ultrathin-walled cellphone components via high-pressure die casting(HPDC).The HPDC AZEX4441 alloy exhibited a fine homogeneous microstructure(average grain size of 2.8μm)with granular Al₁₁RE₃,fibrous Al₂REZn₂,and networked Ca₆Mg₂Zn₃ phases distributed at the grain boundaries.The room-temperature thermal conductivity of the HPDC AZEX4441 alloy was 94.4 W·m^-1·K^-1,which was much higher than 53.7 W·m^-1·K^-1 of the HPDC AZ91D alloy.Al and Zn in the AZEX4441 alloy were largely consumed by the formation of Al₁₁RE₃,Al₂REZn₂,and Ca₂Mg₆Zn₃ phases because of the addition of RE and Ca.Therefore,the lattice distortion induced by solute atoms of the AZEX4441 alloy(0.171%)was much lower than that of the AZ91D alloy(0.441%),which was responsible for the high thermal conductivity of the AZEX4441 alloy.The AZEX4441 alloy exhibited a high yield strength of~185 MPa,an ultimate tensile strength of~233 MPa,and an elongation of~4.2%.This result indicated that the tensile properties were comparable with those of the AZ91D alloy.Therefore,this study contributed to the development of high-performance Mg alloys with a combination of high thermal conductivity,high strength,and good castability.     

铈对AZ31镁合金铸态组织的影响

研究了Ce对AZ31镁合金铸态组织的影响.研究结果表明:添加0.5～1.5 wt%Ce到AZ31镁合金中不但不能细化舍金的晶粒,反而使合金的晶粒变得粗大,并且粗化趋势受Ce加入量的影响较大.当添加0.5 wt%Ce到AZ31镁合金中后,合金的平均晶粒尺寸从最初的60靘增大到164靘.此后,随着Ce加入量从0.5 wt%增加到1.5 wt%,合金的平均晶粒尺寸又开始逐渐减小,但仍大于未添加Ce合金的平均晶粒尺寸.     

Reaction mechanism for in-situ β-SiAlON formation in Fe3Si-Si3N4-Al2O3 composites

In this work, Fe₃Si-Si₃N₄-Al₂O₃ composites were prepared at 1300℃ in an N₂ atmosphere using fused corundum and tabular alumina particles, Al₂O₃ fine powder, and ferrosilicon nitride (Fe₃Si-Si₃N₄) as raw materials and thermosetting phenolic resin as a binder. The effect of ferrosilicon nitride with different concentrations (0wt%, 5wt%, 10wt%, 15wt%, 20wt%, and 25wt%) on the properties of Fe₃Si-Si₃N₄-Al₂O₃ composites was investigated. The results show that the apparent porosity varies between 10.3% and 17.3%, the bulk density varies from 2.94 g/cm3 and 3.30 g/cm3, and the cold crushing strength ranges from 67 MPa to 93 MPa. Under the experimental conditions, ferrosilicon nitride, whose content decreases substantially, is unstable; part of the ferrosilicon nitride is converted into Fe₂C, whereas the remainder is retained, eventually forming the ferrosilicon alloy. Thermodynamic assessment of the Si₅AlON₇ indicated that the ferrosilicon alloy accelerated the reactions between Si₃N₄ and α-Al₂O₃ fine powder and that Si in the ferrosilicon alloy was nitrided directly, forming β-SiAlON simultaneously. In addition, fused corundum did not react directly with Si₃N₄ because of its low reactivity.     

Influence of laser scanning speed on Cu-Zr-Al composite coatings on Mg alloys

To improve the surface properties of magnesium alloys, a study was conducted on Cu-Zr-Al composite coatings on AZ91HP magnesium alloy by laser cladding. The influence of laser scanning speed on the microstructures and properties of the coatings was discussed. The coatings consist of amorphous phase, Cu8Zr3, and Cu10Zr7. With the increase of laser scanning speed, the amorphous phase content of the coatings increases and reaches 60.56wt% with the laser scanning speed of 2.0 m/min. Because of the influence of laser scanning speed on the amorphous and crystal phases, the coatings show the maximum elastic modulus, hardness, and wear resistance at the laser scanning speed of 1.0 m/min. At the laser scanning speed of 2.0 m/min, the coatings have the best corrosion resistance.     

Effects of Sn addition on microstructure and mechanical properties of Mg- Zn-Al alloys

The effects of Sn addition(0, 0.5, 1.0, 2.0 and 3 wt%) on microstructure of Mg-4Zn-1.5Al alloy in cast and extruded states were investigated, and the mechanical properties of as-extruded Mg-4Zn-1.5Al-xSn studied. The experimental results showed that the as-cast Mg-4Zn-1.5Al alloy was composed of two phases α-Mg and Mg_(32)(Al, Zn)_(49), while Sn-containing alloys consisted of α-Mg, Mg_(32)(Al, Zn)_(49) and Mg_2Sn phases, and Mg_(32)(Al, Zn)_(49) was not detected after extruding due to that the most of them dissolved into the matrix during the homogenized treatment. The addition of Sn refined the grains of as-cast and as-extruded Mg-Zn-Al alloys obviously. It was noted that the basal texture intensity reduced with increasing Sn content significantly in as-extruded Mg-Zn-Al alloys. The tensile tests results indicated that Sn addition improve the tensile strength of the extruded alloys,while it had a harmful effect on the ductility. When the addition of Sn was 2 wt%, the ultimate tensile strength(UTS), yield strength(YS) and elongation(ε_f) of the alloy were 280 MPa, 147 MPa and 17.4%, respectively.