Combined Effects of Pre-deformation and Preaging on the Mechanical Properties of Al-Cu-Mg Alloy with Sc and Zr Addition

The combined effects of pre-deformation and pre-aging on the mechanical properties of AlCu-Mg alloy with Sc and Zr addition were investigated. It is revealed that the introduction of pre-deformation can enhance the peak-aging strength, as well as tensile and yield strength, effectively due to the formation of finer and more dispersive precipitation. Pre-aging process before pre-deformation can increase the elongation while maintaining higher strength with a discontinuous distribution of precipitates at grain boundary. The precipitates of bean-like Al3（Sc, Zr） particles further strengthen the alloy via pinning the dislocations which are formed during pre-deformation process and hindering the dislocation motion. Furthermore, pre-deformation and pre-aging accelerate the kinetics of precipitation due to preferential sites provided by the dislocation and the increase of GPB zones＇ size and distribution. The synergism of pre-deformation and pre-aging achieves a combination of better mechanical properties and shorter peak-aging time.

Effect of Trace Sc and Zr on the Mechanical Properties and Microstructure of A1 Alloy 2618

An experimental 2618(Al-Cu-Mg-Fe-Ni) alloy added with trace Sc and Zr was prepared by ingot metallurgy (IM) method. The aging behavior of the alloy was studied by Vickers hardness measurement at 200℃ and 300℃. and the tensile properties of alloy specimens were measured at 20℃, 200℃, 250℃ and 300℃. The microstructure was observed by using optical microscope, SEM and TEM. It was found that the addition of Sc and Zr to 2618 alloy resulted in a primary Al_3(Sc,Zr) phase which could refine the grain because it acts as nuclei of heterogeneous crystallization in the melt during solidification. The secondary Al_3(Sc,Zr) particles were full coherent with matrix and had obvious precipitation hardening effect. They also made the S' phase precipitate more homogeneous. So the strength of alloy increases at both ambient and elevated temperatures without a decrease of ductility. The ductile fracture of alloy occurs by microvoid nucleation, growth and coalescence, so the microvoid coalescence is the dominant fracture mechanism.

Effects of scandium and zirconium combination alloying on as-cast microstructure and mechanical properties of Al-4Cu-1.5Mg alloy

The influences of minor scandium and zirconium combination alloying on the as-cast microstructure and mechanical properties of Al-4Cu-1.5Mg alloy have been experimentally investigated.The experimental results show that when the minor elements of scandium and zirconium are simultaneously added into the Al-4Cu-1.5Mg alloy,the as-cast microstructure of the alloy is effectively modified and the grains of the alloy are greatly refined.The coarse dendrites in the microstructure of the alloy without Sc and Zr additions are refined to the uniform and fine equiaxed grains.As the additions of Sc and Zr are 0.4% and 0.2%,respectively,the tensile strength,yield strength and elongation of the alloy are relatively better,which are 275.0 MPa,176.0 MPa and 8.0% respectively.The tensile strength is increased by 55.3%,and the elongation is nearly raised three times,compared with those of the alloy without Sc and Zr additions.

Microstructure and mechanical properties of Al-5.8Mg-Mn-Sc-Zr alloy after annealing treatment

An A1-5.8Mg-0.4Mn-0.35（Sc＋Zr） （mass fraction, %） alloy sheet was prepared using water chilling copper mould ingot metallurgy processing which was protected by active flux. The influence of stabilizing annealing on mechanical properties and microstructure of the cold rolling sheet was studied. The results show that the strength and hardness of the alloy decrease, while the elongation increases with increasing the stabilizing annealing temperature. With the increase of stabilizing annealing time, the strength and hardness of the alloy drop slightly but its ductility exhibits no change. Partial recovery and recrystallization orderly occur with the increase of annealing temperature during stabilizing treatment. Only different degrees of recovery occur in the alloys annealed below 400 ℃ for 1 h. Partial recrystallization occurs after annealed at 450 ℃ for 1 h. By annealing at 300 ℃ for 1 h, the alloy can obtain the optimum application values of δb, δ0.2 and δ, which are 436 MPa, 327 MPa and 16.7%, respectively.

Effects of minor Sc and Zr additions on mechanical properties and microstructure evolution of Al−Zn−Mg−Cu alloys

The effects of minor Sc and Zr additions on the mechanical properties and microstructure evolution of Al Zn Mg Cu alloys were studied using tensile tests, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The ultimate tensile strength of the peak-aged Al Zn Mg Cu alloy is improved by about 105 MPa with the addition of 0.10% Zr. An increase of about 133 MPa is observed with the joint addition of 0.07% Sc and 0.07% Zr. For the alloys modified with the minor addition of Sc and Zr (0.14%), the main strengthening mechanisms of minor addition of Sc and Zr are fine-grain strengthening, sub-structure strengthening and the Orowan strengthening mechanism produced by the Al3(Sc,Zr) and Al3Zr dispersoids. The volume of Al3Zr particles is less than that of Al3(Sc,Zr) particles, but the distribution of Al3(Sc,Zr) particles is more dispersed throughout the matrix leading to pinning the dislocations motion and restraining the recrystallization more effectively.

Effect of minor Sc and Zr on microstructures and mechanical properties of Al-Zn-Mg based alloys

Two kinds of Al Zn Mg based alloys with and without Sc, Zr addition were prepared by ingot metallurgy. The tensile mechanical properties and microstructures of the studied alloys at different treatment conditions were studied. The results show that addition of minor Sc and Zr can remarkably improve the strength of Al Zn Mg based alloys, but the ductility remains on a higher level. The strength increment is mainly due to fine grain strengthening, substructure strengthening and precipitation strengthening of Al 3(Sc,Zr).

Effect of Sc and Zr on microstructures and mechanical properties of as-cast Al-Mg-Si-Mn alloys

Microstructures of as-cast Al-Mg-Si-Mn alloys with and without Sc and Zr were investigated by optical microscopy, scanning electronic microscopy(SEM) and energy dispersion spectrum analysis. Addition of 0.2%-0.4% Sc can refine the grain size and change the growth morphology from dendritic to fine equi-axial crystal. The higher the addition of Sc, the finer the as-cast grain size. The tensile strength is increased by more than 30% with 0.4% Sc. Moreover, an addition of 0.1%-0.2% Zr is able to refine grain size and change the growth morphology from dendritic to equi-axial grain too, but less effective. However, Zr is found to increase the ductility of the cast alloys, and the elongation is increased to 11.97% with 0.2% Zr.

Atomic bonding and mechanical properties of Al-Mg-Zr-Sc alloy

The valence electron structures of Al-Mg alloy with minor Sc and Zr were calculated according to the empirical electron theory（EET） in solid. The results show that because of the strong interaction of Al atom with Zr and Sc atom in melting during solidification, the Al3Sc and Al3(Sc1-xZrx) particles which act as heterogeneous nuclear are firstly crystallized in alloy to make grains refine. In progress of solidification, the Al-Sc, Al-Zr-Sc segregation regions are formed in solid solution matrix of Al-Mg alloy owing to the strong interaction of Al atom with Zr, Sc atoms in bulk of alloy, so in the following homogenization treatment, the finer dispersed Al3Sc and (Al3(Sc1-xZrx)) second-particles which are coherence with the matrix are precipitated in the segregation region. These finer second-particles with the strong Al—Zr, Al—Sc covalent bonds can strengthen the covalent bonds in matrix of the alloy, and also enhance the hardness and strength of Al-Mg alloy. Those finer second-particles precipitated in interface of sub-grains can also strengthen the covalence bonds there, and effectively hinder the interface of sub-grains from migrating and restrain the sub-grains from growing, and cause better thermal stability of Al-Mg alloy.

Effect of minor Sc and Zr addition on microstructures and mechanical properties of Al-Zn-Mg-Cu alloys

Three kinds of Al-Zn-Mg-Cu based alloys with 0.22%, 0.36%(Sc+Zr) (mass fraction, %), and without Sc, Zr addition were prepared by ingot metallurgy. By using optical microscopy, transmission electronic microscopy and scanning electron microscopy, the effects of microalloying elements of Sc, Zr on the microstructure of super-high-strength Al-Zn-Mg-Cu alloys related to mechanical properties were investigated. The tensile properties and microstructures of the studied alloys under different heat treatment conditions were studied. The addition of minor Sc, Zr results in the formation of Al3(Sc,Zr) particles. These particles are highly effective in refining the microstructures, retarding recrystallization, pinning dislocations and subboundaries. The strength of Al-Zn-Mg-Cu alloys was greatly improved by simultaneously adding minor Sc, Zr, meanwhile the ductility of the studied alloys remains at a higher level. The 0.36%(Sc+Zr) alloys gain the optimal properties after 465 ℃/h solution and 120 ℃/24 h aging. The increment of strength is mainly due to strengthening of fine grain and substructure and precipitation of Al3(Sc, Zr) particles.

Effect of minor Sc and Zr on microstructure and mechanical properties of Al-Zn-Mg-Cu alloy

A series of Al-8.2Zn-2.1Mg-2.3Cu based as-cast alloys and some plates with thickness of 4 mm containing minor Sc and Zr were prepared. The effect of joint addition of minor Sc and Zr on microstructure and mechanical properties of Al-Zn-Mg-Cu alloys were investigated by using OM, SEM with EDS and TEM. The results show that by adding 0.18% Zr (mass fraction) in the cast alloy, the grains can be refined to a certain degree, and by adding 0.18% Sc a little as well. Adding Sc and Zr can generate strong grain refinement effect and obtain a fine equiaxed grain structure, because primary Al3(ScxZr1- )precipitation forms in front of the x a-Al grains. The microstructure and tensile test results show that 0.18% addition of Zr does not bring higher tensile strength and elongation to the alloy of adding Sc, but a better inhibition to recrystallization. Recrystallization inhibiting effect is the strongest in the alloys with joint addition of Sc and Zr. When the content of Zr is unchanged, the strength and elongation of the alloys increase with increasing Sc addition. The increase of strength and elongation in the alloys is related to the refine grain strengthening, precipitation particles strengthening and substructure strengthening principles.

Effects of micro-alloying with Sc and Mn on microstructure and mechanical properties of Al-Mg based alloys

An extensive investigation was made on the effects of micro-alloying with small amounts of Sc and Mn on the microstructure and mechanical properties of the Al-Mg based alloys. It is found that the micro-alloying can significantly enhance the tensile strength of the alloys, and eliminate the dendritic cast structure in it. Many fine, spherical and dispersive Al3Sc particles are found in the annealed Al-Mg-Mn-Sc alloys, which can strongly pin up dislocations and subgrain boundaries, thus strongly retarding the recrystallization of the alloys. The strengthening of the micro-alloyed Al-Mg alloys is attributed to the precipitation strengthening by the Al3Sc particles and to the substructure strengthening.

Effects of minor Sc on microstructure and mechanical properties of Al-Zn-Mg-Zr alloy welded joint

Two kinds of Al-6.0Zn-2.0Mg-0.12Zr and Al-6.0Zn-2.0Mg-0.2Sc-0.12Zr alloy plates were prepared by ingot-metallurgy. The alloy plates with 3 mm thickness were welded by argon shield welding method,and the mechanical properties and microstructures of the two welded joints filled with Al-Mg-Sc welding wire were studied comparatively. The results show that firstly,minor Sc can raise the mechanical properties of the Al-Zn-Mg-Zr base alloy greatly. The reason for the increment is the fine grain strengthening,precipitation strengthening and the substructure strengthening caused by Al3(Sc,Zr). Secondly,η′ phase(MgZn2) and grain size in the heat-affected zone of the alloy without Sc become coarse obviously,the η′ phase(MgZn2) in the heat-affected zone of the alloy with Sc becomes coarse also,but the grain size has no visible change. Al3(Sc,Zr) particles are rather stable and can inhibit the movement of dislocation and sub-grain boundaries,overaging softening is not serious. Thirdly,adding minor Sc can raise the strength of welded joint remarkably,the tensile strength of alloy with Sc increases from 395 MPa to 447 MPa and the welding coefficient increases from 0.7 to 0.8 as well. The reason for the high strength of welded joint with Sc addition is the fine grain strengthening,precipitation strengthening and the increasing of resistance to thermal cycling softening caused by Al3(Sc,Zr).

Effect of pre-deformation on microstructures and mechanical properties of high purity Al-Cu-Mg alloy

The effects of pre-deformation following solution treatment on the microstructure and mechanical properties of aged high purity Al-Cu-Mg alloy were studied by tensile test, micro-hardness measurements, transmission electron microscopy and scanning electron microscopy. The micro-hardness measurements indicate that compared with un-deformed samples, the peak hardness is increased and the time to reach peak hardness is reduced with increasing pre-strain. Additionally, a double-peak hardness evolution behavior of cold-rolled （CR） samples was observed during aging. The results of TEM observation show that the number density of S′（Al2CuMg） phase is increased and the size is decreased in CR alloy with increase of pre-strain. The peak hardness and peak strength of the CR alloy are increased because of quantity increasing and refinement of S′ phase and high density dislocation.

Influence of Zr content on microstructure and mechanical properties of implant Ti-35Nb-4Sn-6Mo-xZr alloys

The influence of Zr content on the microstructure and mechanical properties of implant Ti-35Nb-4Sn-6Mo-xZr （x=0, 3, 6, 9, 12, 15; mass fraction） alloys was investigated. It is shown that Ti-35Nb-4Sn-6Mo-xZr alloys appear to have equiaxed single β microstructure after solution treatment at 1023 K. It is found that the grains are refined first and then coarsened with the increase of Zr content. It is also found that Zr element added to titanium alloys has both the solution strengthening and fine-grain strengthening effect, and affects the lattice parameters. With increasing the Zr content of the alloys, the strength increases, the elongation decreases, whereas the elastic modulus firstly increases and then decreases. The mechanical properties of Ti-35Nb-4Sn-6Mo-9Zr alloy are as follows： σb=785 MPa, δ=11%, E=68 GPa, which is more suitable for acting as human implant materials compared to the traditional implant Ti-6Al-4V alloy.

Effect of Mineral Oil on the Mechanical Properties and Fractographs of Fe_3(Al,Cr,Zr) Intermetallic Alloy

The effect of mineral oil on the mechanical properties and fractographs of Fe3(Al,Cr,Zr) in termetallic alloy has been investigated. The results show that the tensile ductility of the Fe3(Al,Cr,Zr) alloy tested in oil is comparable with the results obtained in oxygen and is in sensitive to strain rate. The fracture mode of the Fe3(Al,Cr,Zr) alloy treated at 700℃/1.5 h and tested in oil, is cleavage and with dimples in some areas.

Effect of heat treatment on microstructures and mechanical properties of sand-cast Mg-10Gd-3Y-0.5Zr magnesium alloy

The microstructure, mechanical properties and fracture behavior of sand-cast Mg-10Gd-3Y-0.5Zr alloy （mass fraction,%） under T6 condition （air cooling after solid solution and then aging heat treatment） were investigated. The optimum T6 heat treatments for sand-cast Mg-10Gd-3Y-0.5Zr alloy are （525 ℃, 12 h＋225 ℃, 14 h） and （525 ℃, 12 h＋250 ℃, 12 h） according to age hardening curve and mechanical properties, respectively. The ultimate tensile strength, yield strength and elongation of the Mg-10Gd-3Y-0.5Zr alloy treated by the two optimum T6 processes are 339.9 MPa, 251.6 MPa, 1.5%and 359.6 MPa, 247.3 MPa, 2.7%, respectively. The tensile fracture mode of peak-aged Mg-10Gd-3Y-0.5Zr alloy is transgranular quasi-cleavage fracture.

Effect of heat treatment on microstructures and mechanical properties of sand-cast Mg-4Y-2Nd-1Gd-0.4Zr magnesium alloy

Influence of heat treatment on the microstructures and mechanical properties of sand-cast Mg-4Y-2Nd-1Gd-0.4Zr magnesium alloy was investigated,and the tensile fracture mechanisms of the studied alloys under different conditions were also discussed.The results show that the optimum T4 and T6 heat treatment conditions for the as-cast Mg-4Y-2Nd-1Gd-0.4Zr alloy are 525°C,8 h and（525°C,8 h）＋（225°C,16 h）,respectively,with regard to the microstructure observation,DSC heating curve and mechanical properties.The hardness,yield strength,ultimate tensile strength and elongation of the Mg-4Y-2Nd-1Gd-0.4Zr alloy treated by optimum T6 heat treatment are HV91,180 MPa,297 MPa and 7.4%,respectively.Moreover,the Mg-4Y-2Nd-1Gd-0.4Zr alloys under different heat treatment conditions exhibit different tensile fracture modes.

Effect of homogenization treatment on microstructure and properties of Al-Mg-Mn-Sc-Zr alloy

The effect of homogenization on the hardness,tensile properties,electrical conductivity and microstructure of as-cast Al-6Mg-0.4Mn-0.25Sc-0.12Zr alloy was studied.The results show that during homogenization as-cast studied alloy has obviously hardening effect that is similar to aging hardening behavior in traditional Al alloys.The precipitates are mainly Al3(Sc,Zr)and Al6Mn.When homogenization temperature increases the hardness peak value is declined and the time corresponding to hardness peak value is shortened.The electrical conductivity of the alloy monotonously increases with increasing homogenization temperature and time.The decomposition of the supersaturated solid solution containing Sc and Zr which is formed during direct chilling casting and the precipitation of Al3(Sc,Zr)cause hardness increasing.The depletion of the matrix solid solubility decreases the ability of electron scattering in the alloy,resulting in the electrical conductivity increased.Tensile property result at hot rolling state shows that the optimal homogenization treatment processing is holding at 300-350 ℃ for 6-8 h.

Microstructures evolution and mechanical properties disparity in 2070 Al-Li alloy with minor Sc addition

The microstructures and mechanical properties of Al-3.35Cu-1.2Li-0.4Mg-0.4Zn-0.3Mn-0.1Zr （mass fraction, %） alloywith Sc addition or free Sc were investigated through tensile test, SEM, EPMA and TEM. The addition of 0.082% （mass fraction） Scelement leads to the formation of Cu-rich and Sc-contained nano-sized Al3（ScZr） particles and W phase particles. The Al3（ScZr）particles can inhibit recrystallization to a certain extent and impede recrystallized grain growth during solution treatment. It is foundthat W phase cannot dissolve in supersaturated solid solution during the solution heat treatment, and the Cu content in thesolutionized matrix is decreased, which causes a decrease in the fraction of Cu-contained strengthening precipitates with T1 （Al2CuLi）and θ＇ （Al2Cu） under T8 aging condition. Due to the formation of the W phases, the small Sc addition causes a little reduction in thestrength.

Effect of Zr modification on solidification behavior and mechanical properties of Mg–Y–RE (WE54) alloy

Magnesium alloys containing rare earth elements (RE) have received considerable attention in recent years due to their high mechanical strength and good heat-resisting performance. Among them, Mg–5%Y–4%RE (WE54) magnesium alloy is a high strength sand casting magnesium alloy for use at temperatures up to 300 ℃, which is of great interest to engineers in the aerospace industry. In the present work, the solidification behavior of Zr-containing WE54 alloy and Zr-free alloy was investigated by computer-aided cooling curve analysis (CA-CCA) technique. And the solidification microstructure and mechanical properties of them were also investigated comparatively. It is found from the cooling curves and as-cast microstructure of WE54 alloy that the nucleation temperature of α-Mg in WE54 alloy increases after Zr addition, and the as-cast microstructure of the alloy is significantly refined by Zr. While the phase constitution of WE54 alloy is not changed after Zr addition. These phenomena indicate that Zr acts as heterogeneous nuclei during the solidification of WE54 alloy. Due to refined microstructure, the mechanical properties of Zr-containing WE54 alloy is much higher than Zr-free WE54 alloy.