Dependence of microstructure and mechanical properties on solidification condition of directionally solidified Zn-55Al-1.6Si alloys

In this study,directional solidification was utilized to explore the relationship between microstructure,mechanical properties,and withdrawal speeds of Zn-55Al-1.6Si alloys.In order to assess the characteristics of Zn-55Al-1.6Si alloys,both the microstructure and mechanical properties were thoroughly analyzed.This involved conducting room temperature tensile tests on samples with different withdrawal speeds(5,10,100,200,and 400μm·s^(-1)).The results reveal that both the as-cast alloy and samples after directional solidification are composed of zinc,aluminum,and silicon phases.As the withdrawal speed increases,an evident decrease in the size of the primary dendrites is observed.The results of tensile experiments show that Zn-55Al-1.6Si alloys after directional solidification exhibit brittle fracture characteristics,both the tensile strength and elongation of the alloys increase with withdrawal speed.

Effects of neodymium addition on microstructure and mechanical properties of near-eutectic Al-12Si alloys

The microstructure and mechanical properties of near-eutectic Al-12 Si alloys modified with 0-0.4% Nd（mass fraction） were investigated. The results indicate that a submicro- or nano-sized Al2 Nd phase is observed in the modified alloy with 0.3% Nd. The morphology of the α（Al） phase is significantly refined in the Nd-modified alloys. The primary Si morphology simultaneously changes into a fine, particle-like morphology, and the morphology of eutectic Si becomes fine-fibrous instead of coarse-acicular. Relatively few growth twins are observed on the surface of the Si plate in the Al-12Si-0.3Nd alloy at the optimal modification level. The mechanical property test results confirm that the mechanical properties of the as-cast Al-12 Si alloys are enhanced after the Nd addition, with optimal ultimate tensile strength（UTS） of 252 MPa and elongation（EL） of 13% at an Nd content of 0.3%. The improved mechanical properties are attributed to the refined morphology of Si phase and the formation of the Al2 Nd phase.

Theoretical prediction of new C–Si alloys in C2/m-20 structure

We study structural,mechanical,and electronic properties of C_（20）,Si_（20） and their alloys（C_（16）Si_4,C_（12）Si_8,C_8Si_（12）,and C_4Si_（16）） in C2/m structure by using density functional theory（DFT） based on first-principles calculations.The obtained elastic constants and the phonon spectra reveal mechanical and dynamic stability.The calculated formation enthalpy shows that the C-Si alloys might exist at a specified high temperature scale.The ratio of BIG and Poisson＇s ratio indicate that these C-Si alloys in C2/m-20 structure are all brittle.The elastic anisotropic properties derived by bulk modulus and shear modulus show slight anisotropy.In addition,the band structures and density of states are also depicted,which reveal that C_（20）,C_（16）Si_4,and Si_（20） are indirect band gap semiconductors,while C_8Si_（12） and C_4Si_（16） are semi-metallic alloys.Notably,a direct band gap semiconductor（C_（12）Si_8） is obtained by doping two indirect band gap semiconductors（C_（20） and Si_（20））.

Effect of Sr modification on microstructure and thermal conductivity of hypoeutectic Al−Si alloys

Trace amount of Sr(0.05 wt.%)was added into the hypoeutectic Al−Si(3−12 wt.%Si)alloys to modify their microstructure and improve thermal conductivity.The results showed that the thermal conductivity of hypoeutectic Al−Si alloys was improved by Sr modification,and the increment and increasing rate of the thermal conductivity gradually increased with Si content increasing.The improvement of thermal conductivity was primarily related to the morphology variation of eutectic Si phases.In Sr-modified Al−Si alloys,the morphology of eutectic Si phases was a mixed morphology of fiber structure and fine flaky structure,and the proportion of the fine flaky eutectic Si phases gradually decreased with Si content increasing.Under the Si content reaching 9 wt.%,the proportion of fine flaky eutectic Si phases was nearly negligible in Sr-modified alloys.Correspondingly,the increment and increasing rate of thermal conductivity of Sr-modified alloys reached the maximum and tended to be stable.

Microstructure and mechanical properties of friction stir processed Al−Mg2Si alloys

The microstructure and mechanical properties of friction stir processed Al−Mg2Si alloys were studied by TEM and EBSD.The results showed that an increase in the tool rotation speed(300−700 r/min)led to a decrease in the defect area(from 10.5 mm2 to zero),whereas the defect area demonstrated the opposite trend(increased to 1.5 mm2 from zero)upon further increasing the rotation speed(700−1200 r/min).The types of defects were transformed from tunnel defects to fusion defects as the rotational speed increased.The coarse Mg2Si dendrites were broken and fine particles(smaller than 10mm)formed in the weld nugget(WN).The amount of low-angle grain boundaries increased significantly from 57.7%to 83.6%,which was caused by an increase in the content of the deformed structure(from 1.7%to 13.6%).The hardness,ultimate tensile strength(UTS)and elongation were all greatly improved for the weld nugget.The hardness values of the WNs had the following order:R300<R1200<R500<R900<R700.The UTS and elongation had the following order:BM(base material)<R300<R1200<R500<R900<R700.The UTS and the elongation for the WN were increased by one and three times,respectively.

Effect of ultrasonic and mechanical vibration treatments on evolution of Mn-rich phases and mechanical properties of Al−12Si−4Cu−1Ni−1Mg−2Mn piston alloys

Effects of ultrasonic vibration(UV)and mechanical vibration(MV)on the Mn-rich phase modification and mechanical properties of Al−12Si−4Cu−1Ni−1Mg−2Mn piston alloys were investigated.The results show that the UV and UV+MV treatments can significantly refine and fragmentize the microstructures.In addition,UV treatment can significantly passivate the primary Mn-rich Al15Mn3Si2 intermetallics.The formation mechanisms of refinement and passivation of the grains and non-dendrite particles were discussed.Compared with the gravity die-cast alloys,the UV and UV+MV treated alloys exhibit improved tensile and creep resistance at room and elevated temperatures.These results can be attributed to the refinement of theα(Al)grains and the secondary intermetallics,the increased proportion of refined heat-resistant precipitates,and the formation of nano-sized Si particles.The ultimate tensile strength of the UV treated alloys at 350℃ exceeds that of commercial piston alloys.This indicates the high application potential of the developed piston alloys in density diesel engines.

Influence of technical parameters on strength and ductility of AlSi9Cu3 alloys in squeeze casting

An orthogonal test was conducted to investigate the influence of technical parameters of squeeze casting on the strength and ductility of AISigCu3 alloys. The experimental results showed that when the forming pressure was higher than 65 MPa, the strength （ab） of A1Si9Cu3 alloys decreased with the forming pressure and pouring temperature increasing, whereas ab increased with the increase of filling velocity and mould preheating temperature. The ductility （6） by alloy was improved by increasing the forming pressure and filling velocity, but decreased with pouring temperature increasing. When the mould preheating temperature increased, the ductility increased first, and then decreased. Under the optimized parameters of pouring temperature 730 ℃, forming pressure 75 MPa, filling velocity 0.50 m/s, and mould preheating temperature 220 ℃, the tensile strength, elongation, and hardness of A1Si9Cu3 alloys obtained in squeeze casting were improved by 16.7%, 9.1%, and 10.1%, respectively, as compared with those of sand castings.

Laser Powder Bed Fusion Processing of Soft Magnetic Fe–Ni–Si Alloys: Effect of Hot Isostatic Pressing Treatment

Laser powder bed fusion(L-PBF)-processed high-silicon steel has great advantages in freely designed electric engines,and various studies have been conducted in this field.However,the analysis of both the mechanical and magnetic properties,focusing on the multiscale microstructure under as-fabricated and heat-treated conditions,which is indispensable for industrial applications,has not been performed.In this study,an Fe–Ni–Si sample was fabricated using the L-PBF process.Subsequently,the following hot isotropic pressing(HIPing)process was employed as a post heat treatment step for the Fe–Ni–Si alloys.The effects of HIPing on the microstructure were investigated,focusing on the metastable stable phase transformation in the Fe–Ni–Si system.X-ray diffraction results showed single-phase fccγ(Fe,Ni)in the L-PBF-processed samples before and after HIPing.Moreover,the acicular Ni/Si-rich structure(formed in the as-fabricated L-PBF sample because of its high cooling rates)transformed to the equilibrium austenite,Ni3Si,and FeNi3 phases during HIPing.After HIP,the compressive modulus and strength increased from 11 GPa and 650 MPa to approximately 18 GPa and 900 MPa,respectively.The magnetic properties were evaluated via a hysteresis loop,and the coercivity increased from 1.8 kA/m and to 2.9 kA/m after the HIPing process.

Effects of Si alloying and T6 treatment on mechanical properties and wear resistance of ZA27 alloys

To improve the mechanical properties and wear resistance of ZA27 alloy, Si was introduced to the alloy, and the effect of Si alloying and T6 heat treatment on the microstructure, mechanical properties and wear resistance was investigated. The results show that with 0.55% Si, the microstructure of the alloy can be refined effectively, which leads to the increase of hardness. But the tensile strength and elongation decrease because Si undermines the integrity of the matrix. On the other hand, the dendrites are transformed into a desired α+η+(α+η)mixture with T6 heat treatment, which introduces a remarkable increase to the elongation and hardness of the alloy. The wear resistance of the ZA27 alloy with Si alloying is significantly better than that of the ZA27 alloy without Si. With the increase of Si addition, the wear resistance of the alloy firstly increases and then decreases.In the alloy without Si alloying, severe plastic deformation and large delamination were observed on the worn surface of the alloy. However, with the increase of Si, the main wear mechanism transformed to abrasive wear gradually. In addition, the T6 treatment can further improve the wear resistance of the alloy with Si alloying.

Mechanical and thermo-physical properties of rapidly solidified Al-50Si-Cu(Mg) alloys for thermal management application

Al-high Si alloys were designed by the addition of Cu or Mg alloying elements to improve the mechanical properties. It is found that the addition of 1 wt.% Cu or 1 wt.% Mg as strengthening elements significantly improves the tensile strength by 27.2% and 24.5%, respectively. This phenomenon is attributed to the formation of uniformly dispersed fine particles(Al2Cu and Mg2Si secondary phases) in the Al matrix during hot press sintering of the rapidly solidified(gas atomization) powder. The thermal conductivity of the Al-50 Si alloys is reduced with the addition of Cu or Mg, by only 7.3% and 6.8%, respectively. Therefore, the strength of the Al-50 Si alloys is enhanced while maintaining their excellent thermo-physical properties by adding 1% Cu(Mg).

Tribological Properties of Nanostructured Al/Al_(12)(Fe,V)_3Si Alloys

Tribological behavior of nanostructured pure Al and Al–Al12（Fe,V）3Si alloys containing 27（FVS0812） and 37（FVS1212） vol% of Al12（Fe,V）3Si precipitates was investigated. All samples were prepared using mechanical alloying followed by hot pressing. Wear tests were performed at room temperature using a pin-on-disk machine. Results showed that the presence of Al12（Fe,V）3Si precipitates increases the wear resistance of nanostructured Al, and the wear resistance increases with increasing the Al12（Fe,V）3Si content. Scanning electron microscopy images of worn surfaces and wear debris demonstrated that abrasion and adhesion are the governing wear mechanisms for the nanostructured FVS0812 alloy at 2 and 5 N normal loads, whereas for the nanostructured FVS1212 alloy, the dominant wear mechanism is abrasion at these loads. A mechanically mixed layer（MML） containing Fe and O was formed on the worn surfaces of FVS0812 and FVS1212 samples at 10 N normal load. Formation and delamination of MML controls the wear behavior of these samples at the normal load of 10 N. It is also found that the presence of Al12（Fe,V）3Si precipitates decreases the friction coefficient of nanostructured Al.

Comparative Study on Wire-Arc Additive Manufacturing and Conventional Casting of Al–Si Alloys:Porosity,Microstructure and Mechanical Property

Here,we compare the porosity,microstructure and mechanical property of 4047 Al–Si alloys prepared by wire-arc additive manufacturing(WAAM)and conventional casting.X-ray microscopy reveals that WAAM causes a higher volume fraction of gas pores in comparison with conventional casting.Effective refi nements ofα-Al dendrites,eutectic Si particles and Ferich intermetallic compounds are achieved by WAAM,resulting from its rapid solidifi cation process.Both ultimate tensile strength(UTS,up to 205.6 MPa)and yield stress(YS,up to 98.0 MPa)are improved by WAAM at the expense of elongation after fracture.The mechanical property anisotropy between scanning direction and build direction is minimal for alloys via WAAM.Additional microstructure refi nement and strength enhancement are enabled by increasing the travel speed of welding torch from 300 to 420 mm/min.

Development of High Strength and Toughness Non-Heated Al–Mg–Si Alloys for High-Pressure Die-Casting

Based on the 3 factors and 3 levels orthogonal experiment method,compositional effects of Mg,Si,and Ti addition on the microstructures,tensile properties,and fracture behaviors of the high-pressure die-casting Al-x Mg-y Si-z Ti alloys have been investigated.The analysis of variance shows that both Mg and Si apparently infl uence the tensile properties of the alloys,while Ti does not.The tensile mechanical properties are comprehensively infl uenced by the amount of eutectic phase(α-Al+Mg2Si),the average grain size,and the content of Mg dissolved intoα-Al matrix.The optimized alloy is Al-7.49 Mg-3.08 Si-0.01 Ti(wt%),which exhibits tensile yield strength of 219 MPa,ultimate tensile strength of 401 MPa,and elongation of 10.5%.Furthermore,contour maps,showing the relationship among compositions,microstructure characteristics,and the tensile properties are constructed,which provide guidelines for developing high strength and toughness Al–Mg–Si–Ti alloys for high-pressure die-casting.

Oxidation and hot corrosion behaviors of Nb−Si based ultrahigh temperature alloys at 900℃

Oxidation and hot corrosion behaviors at 900 ℃ of Nb-Si based ultrahigh temperature alloys were investigated. Both oxidation and hot corrosion kinetics curves of the alloy involve an initial parabolic stage and a later rapid linear stage. In the initial oxidation stage(1-50 h), a thin and continuous scale is formed on the alloy surface, while severe pest degradation phenomenon is observed in the linear oxidation stage. Compared with oxidation of the alloy in static air, a linear hot corrosion stage happens earlier and catastrophic scale disintegration occurs after hot corrosion for 20-100 h, demonstrating that molten salts(Na2SO4 and NaCl) could significantly accelerate the oxidation process of the alloy. STEM results indicate that the corroded scale consists mainly of TiO2, Nb2O5, TiNb2O7, amorphous silicate and NaNbO3.

Weldability and Microstructure of Nickel-Silicon Based Alloys

The NiSix based alloy typically has poor weldability due to its lower ductility. A limited amount of work has been performed on the weldability of NiSix based alloys. Therefore, the effect of heat treatment and welding parameters on weldability of the alloys, and the relationship between the weldability and microstructure were studied. The results show that the as-cast Ni-Si-Nb-B alloy （Ni 76. 5%, Si 20%, Nb 3%, and B 0. 5%） could be successfully welded after preheating at 600 ℃. The welding procedure should be performed on the alloys before any heat treatment and a preheating at 600 ℃ should be used. The fusion zone is harder than the matrix due to a large amount of 7 phase and a finer microstructure. The cracks are predominantly intergranular in heat affected zone and associated with the needle-like ）, phase. The heat treatment before welding increases the tendency of cracking in the fusion zone.

Microstructure and mechanical properties of Cu/Al joints brazed using(Cu,Ni,Zr,Er)-modified Al−Si filler alloys

To design a promising Al−Si filler alloy with a relatively low melting-point,good strength and plasticity for the Cu/Al joint,the Cu,Ni,Zr and Er elements were innovatively added to modify the traditional Al−Si eutectic filler.The microstructure and mechanical properties of filler alloys and Cu/Al joints were investigated.The result indicated that the Al−Si−Ni−Cu filler alloys mainly consisted of Al(s,s),Al_(2)(Cu,Ni)and Si(s,s).The Al−10Si−2Ni−6Cu filler alloy exhibited relatively low solidus(521℃)and liquidus(577℃)temperature,good tensile strength(305.8 MPa)and fracture elongation(8.5%).The corresponding Cu/Al joint brazed using Al−10Si−2Ni−6Cu filler was mainly composed of Al_(8)(Mn,Fe)_(2)Si,Al_(2)(Cu,Ni)3,Al(Cu,Ni),Al_(2)(Cu,Ni)and Al(s,s),yielding a shear strength of(90.3±10.7)MPa.The joint strength was further improved to(94.6±2.5)MPa when the joint was brazed using the Al−10Si−2Ni−6Cu−0.2Er−0.2Zr filler alloy.Consequently,the(Cu,Ni,Zr,Er)-modified Al−Si filler alloy was suitable for obtaining high-quality Cu/Al brazed joints.

Wettability of CuNi-Ti Alloys on Si_3N_4 and Interfacial Reaction Products

Based on the alloy Cu55Ni45 (at pct), holding the proportion of Cu to Ni in constant and in the temperature range of 1233~1573 K, the wetting angles of CuNi-0~56 at pct Ti alloys on Si3N4 have been measured by the sessile drop method. With the increase of Ti content, the wetting angles decreased. The equilibrium wetting angle was 5° when Ti content ≥32 at pct.In the case of same Ti content, the activity of Ti in CuNiTi alloy was weaker than that in CuTi alloy The cross-section of the CuNiTi-Si3N4 interface and the elements distribution were examined by scanning electron microscope with X-ray wave-dispersion spectrometer, and the reaction products formed at the interface were determined by X-ray diffiaction analysis method.

Effect of Deformation Temperature on Deformation Mechanism of Fe-6.5Si Alloys with Different Initial Microstructures

Deformation behaviors and mechanisms under different temperatures for columnar-grained Fe 6.5Si （mass%） alloys fabricated by directional solidification and equiaxed grained Fe-6.5Si alloy fabricated by forging were comparatively investigated. The results showed that, with increasing the deformation temperature from 300℃ to 500℃, the elongation increased from 2.9% to 30.1% for the equiaxed-grained Fe-6.5Si alloy, while from 6.6% to about 51% for the columnar-grained Fe-6.5Si alloy. The deformation mode of equiaxed-grained Fe 6.5Si alloy trans ferred from nearly negligible plastic deformation to large plastic deformation dominated by dislocation slipping. Comparatively, the deformation mode of the columnar grained alloy transferred from nearly negligible plastic deformation to plastic deformation dominated by the twining, and finally to plastic deformation dominated by dislocation slipping. Meanwhile, compared with the alloy with equiaxed grains, it was found that ultimate tensile strength and elongation could be increased simultaneously, which was ascribed for the twinning deformation in columnar-grained Fe-6.5Si al loy. This work would assist us to further understand the plastic deformation mechanism of Fe-6.5Si alloy and pro vide more clues for high-efficiency production of the alloy.

Effects of Cu addition on microstructure and mechanical properties of Er-modified Al-10Mg_(2)Si cast alloys

The solidification microstructure and mechanical properties of hypoeutectic Al-10Mg_(2)Si cast alloys with different Cu contents and 0.45 wt.% Er were investigated using an optical microscope, scanning electron microscope, and an electronic universal testing machine. Results showed that Cu and Er could significantly reduce the grain size of the eutectic Mg;Si phase from 15.4 μm for the base alloy to 5.8 μm for the alloy with 1.5 wt.% Cu and 0.45 wt.% Er.Meanwhile, the needle-like β-Al5Fe Si phase was modified to fine sized irregular shaped Cu, Er and Fe-rich particles with the additions of Cu and Er. The strength and ductility of the Al-10Mg_(2)Si as-cast alloys were simultaneously improved by the additions of Cu and Er, and the ultimate tensile strength, yield strength and elongation increase from 223 MPa,136 MPa and 2.1% to 337 MPa, 169 MPa and 4.7%, respectively. The heterogeneous nucleation of Mg_(2)Si on Al P was avoided by forming Cu, Er and P-containing phases, due to the additions of Cu and Er. Moreover, the Cu and Er atomic clusters and their intermetallic segregated on the surface of the eutectic Mg_(2)Si and inhibited the growth of the eutectic Mg_(2)Si, which were responsible for the modification of the eutectic Mg_(2)Si.

Influence of Neodymium on Amorphizability of RS Al-Fe-V-Si-Nd Alloys:An Investigation Using Time Dependent Nucleation Theory

Time dependent nucleation theory was applied to calculate the incubation time required for α Al nucleation in rapid solidified (RS) Al Fe V Si Nd alloys. The nucleation rates were calculated as a function of temperature, and the critical cooling rates required for the formation of amorphous α Al at different neodymium concentrations were calculated too. The addition of neodymium increases the amorphizablity of α Al by increasing the incubation time and decreasing the nucleation rate and the critical cooling rate. The calculations are fitted to experimental results when liquidus temperatures are estimated from an approximation, which treats Al Fe V Si Nd as quasi binary Al Fe system.