Microstructure and impact behavior of Mg-4Al-5RE-xGd cast magnesium alloys

This work investigated the microstructure and impact behavior of Mg-4Al-5RE-xGd(RE represents La-Ce mischmetal;x=0,0.2,0.7 wt.%)alloys cast by high-pressure die casting(HPDC),permanent mold casting(PMC),and sand casting(SC)techniques.The results indicated that with increasing Gd content,the grain sizes of the HPDC alloy had a slight change,but the grains of the PMC and SC alloys were significantly refined.Besides,the acicular Al_(11)RE_(3)phase was modified into the short-rod shape under the three casting conditions.The impact toughness of the studied alloy was mainly dominated by the absorbed energy during the crack initiation.With increasing Gd content,the impact toughness of the studied alloy monotonically increased due to the lower tendency of the modified second phase toward crack initiation.The impact stress was higher than the tensile stress,exhibiting a strain rate sensitivity for the mechanical response;however,the HPDC alloy had an inconsistent strain rate sensitivity during the impact event due to the transformation of the deformation mechanism from twinning to slip with increasing strain.Abundant dimples covered the fracture surface of the fine-grained HPDC alloys,indicating a typical ductile fracture.Nevertheless,due to the deficient{1012}twinning activity and the suppressed grain boundary sliding during the impact event,the HPDC alloys showed insufficient plastic deformation capacity.

Damping performance of SiC nanoparticles reinforced magnesium matrix composites processed by cyclic extrusion and compression

This work dealt with the damping performance and its underlying mechanism in SiC nanoparticles reinforced AZ91D composite(SiC_(np)/AZ91D)processed by cyclic extrusion and compression(CEC).It was found that the CEC process significantly affects the damping performance of the composite due to alterations in the density of dislocations and grain boundaries in the matrix alloy.Although there would be dynamic precipitation of the Mg17Al12 phase during processing which increases the phase interface and limits the mobility of dislocations and grain boundaries.The results also showed that the damping capacity of 1%SiC_(np)/AZ91D composite continuously decreases with adding CEC pass number and it consistently increases with rising the applied temperature.Considering the first derivative of the tanδ-T curve,the dominant damping mechanism based on test temperature can be divided into three regions.These three regions are as follows(i)dislocation vibration of the weak pinning points(≤T_(cr)),(ii)dislocation vibration of the strong pinning points(T_(cr)∼T_(V)),and(iii)grain boundary/interface sliding(≥T_(V))

Enhancing mechanical properties and corrosion performance of AA6063 aluminum alloys through constrained groove pressing technique

The use of a constrained groove pressing(CGP) method to plastically deform AA6063 aluminum alloy led to the improved surface properties. It was found that hardness magnitude is dramatically improved and its uniformity is considerably decreased after the first pass, while subsequent passes result in better hardness behavior for the processed material. Also, the elongated grains formed in the first pass of the CGP are gradually converted to the equiaxed counterparts by adding pass numbers. Eventually, higher corrosion resistance of the sample by imposing the CGP process is related to the quick formation of passivation film and the change in the morphology of the second phase and precipitates which hinder their electrochemical reactions and decrease the potential localized attack sites.

Microstructure and mechanical properties of squeeze-cast Al−5.0Mg−3.0Zn−1.0Cu alloys in solution-treated and aged conditions

The microstructure and mechanical properties at different depths of squeeze-cast,solution-treated and aged Al−5.0Mg−3.0Zn−1.0Cu alloy were investigated.For squeeze-cast alloy,from casting surface to interior,the grain size ofα(Al)matrix and width of T-Mg32(AlZnCu)49 phase increase significantly,while the volume fraction of T phase decreases.The related mechanical properties including ultimate tensile strength(UTS)and elongation decrease from 243.7 MPa and 2.3%to 217.9 MPa and 1.4%,respectively.After solution treatment at 470℃ for 36 h,T phase is dissolved into matrix,and the grain size increases so that the UTS and elongation from surface to interior are respectively reduced from 387.8 MPa and 18.6%to 348.9 MPa and 13.9%.After further peak-aging at 120℃ for 24 h,numerous G.P.II zone andη′phase precipitate in matrix.Consequently,UTS values of the surface and interior increase to 449.5 and 421.4 MPa,while elongation values decrease to 12.5%and 8.1%,respectively.

Review on corrosion resistance of mild steels in liquid aluminum

The corrosion of mild steels by liquid aluminum is an intractable issue in aluminum industry.This review aims to provide an overview of the corrosion behavior of mild steels in the static liquid aluminum with an emphasis on the thermodynamic and kinetic aspects.The corrosion mechanisms of mild steels in liquid aluminum are discussed systematically,based on which four corrosion control approaches including alloying,introducing secondary phase,matrix microstructure control and surface treatment are introduced.Currently,a combination of improvement approaches may have a great potential for further enhancement in corrosion resistance.

Segregation behavior and its regulating process in as-cast magnesium alloy containing heavy rare earth

Specific gravity segregation that occurs during the smelting process always leads to the low composition homogeneity and poor performance stability of the magnesium-rare earth(Mg-RE)alloys.In this study,the segregation behavior of Mg-Gd alloy was investigated by sampling from different locations in the ingot fabricated in a resistance furnace without a pouring process.The combined application of induction-heating and mechanical stirring with various speeds(0-130 r/min)was applied to promote the distribution homogeneity of Gd atoms.In the resistance-heating fabricated ingot,Gd content at the bottom section reaches 407%of that at the top.The coarse dendrites surrounded by the network-like eutectic structures are responsible for the brittle fracture with a poor elongation of 3.7%.By the combined employment of the induction heating and mechanical stirring with the speed of 87 r/min at 740℃for 40 s,the variation of the Gd content within the whole ingot can be reduced to be the minimum of 0.23 wt%.Corresponding formation and regulating models of segregation were also proposed.However,the cooling rate of the melt is reduced by the continuous increase of the stirring speed to 130 r/min,which results in the grain coarsening and lower homogeneity of the ingot.

Effects of Gd Addition on the Microstructure and Tensile Properties of Mg–4Al–5RE Alloy Produced by Three Different Casting Methods

This work deals with the effect of 0.67 wt%Gd addition on the microstructure and tensile properties of Mg–4 Al–5 RE(where RE represents La–Ce mischmetal)alloy produced by sand casting(SC),permanent mold casting(PMC),and high-pressure die casting(HPDC).The results show that Gd addition could refine the grains,but its efficiency decreases by increasing the cooling rate due to the shifting from SC to PMC and finally to the HPDC method.Meanwhile,the acicular Al11 RE3 phase is modified into the short-rod or granular-like shape under the three casting conditions.Such refined and modified microstructures are due to the Al2(Gd,RE)phases,which act as the nucleation sites in both theα-Mg matrix and Al11 RE3 phase.Also,the weakening grain refinement effect in the increased cooling rates can be attributed to the narrow constitutional undercooling zone.After Gd addition,the 0.2%proof strength of the SC and PMC alloys increases by about 16.9%and 12.7%,respectively,while in the HPDC alloy,it decreases by about 5.9%.The main factor in the strength increment of the SC and PMC alloys is the grain boundary strengthening due to grain refinement which is proved by modeling the related mechanisms,whereas weak secondary phases and grain boundary strengthening mechanisms in the HPDC alloy lead to strength reduction.After Gd addition,the elongation to failure of the SC,PMC,and HPDC alloys is significantly enhanced by about 34.8%,20.2%,and 12.3%,respectively,due to the crack resistance nature of the modified short-rod/granular Al11(RE,Gd)3 phase compared to the acicular one.

Route Effect on Equal Channel Angular Pressing of Copper Tube

A new technique to produce ultra-fine grained tubular specimen has been proposed, and the experiments have been performed using equal channel angular pressing （ECAP） with an angle of 90 between two intersecting channels and also the use of rubber pad as a mandrel during process. Commercial purity copper tubes have been pressed up to three passes through four different fundamental routes （A, BA, Bc, and C） directions of which are identified in the text below. The influence of each route on the value, distribution, and homogeneity of hardness has been investigated by applying Vickers micro-hardness measurements at various locations of the tube＇s transverse planes. Significant enhancement of the hardness is observed after the first pass ECAP. Also, routes C and Bc show, respectively, better average hardness magnitude and hardness distribution uniformity. In addition, the results indicate that there is about 50% and 62% reduction of the grain size, compared to the annealed condition, following ECAP process of the copper tube sample after the first and the third pass via route Bc.

Highly sensitive determination of promazine in pharmaceutical and biological samples using a ZnO nanoparticle-modified ionic liquid carbon paste electrode

In this work we describe the first report for the determination of promazine using a nanostructure- modified ionic liquid carbon paste electrode in aqueous solutions. To achieve this goal, a novel modified carbon paste electrode using ZnO nanoparticles and l-methyl-3-butylimidazolium bromide as a binder （ZnO/NPs/ILs/CPE） was fabricated. The oxidation peak potential of promazine at the surface of the ZnO/ NPs/ILs/CPE appeared at 685 mV, which was about 65 mV lower than the oxidation potential at the surface of CPE under similar conditions. Also, the peak current was increased to about 4.0 times higher at the surface of ZnO/NPs/ILs/CPE compared to that of CPE. The linear response range and detection limit were found to be 0.08-450 and 0.04 μmol/L, respectively. The modified electrode was successfully used for the determination of promazine in real samples with satisfactory results.