Effect of cold rolling deformation on microstructure evolution and mechanical properties of spray formed Al−Zn−Mg−Cu−Cr alloys

The impact of cold rolling deformation,which was introduced after solid solution and before aging treatment,on microstructure evolution and mechanical properties of the as-extruded spray formed Al−9.8Zn−2.3Mg−1.73Cu−0.13Cr(wt.%)alloy,was investigated.SEM,TEM,and EBSD were used to analyze the microstructures,and tensile tests were conducted to assess mechanical properties.The results indicate that the D1-T6 sample,subjected to 25%cold rolling deformation,exhibits finer grains(3.35μm)compared to the D0-T6 sample(grain size of 4.23μm)without cold rolling.Cold rolling refines the grains that grow in solution treatment.Due to the combined effects of finer and more dispersed precipitates,higher dislocation density and smaller grains,the yield strength and ultimate tensile strength of the D1-T6 sample can reach 663 and 737 MPa,respectively.In comparison to the as-extruded and D0-T6 samples,the yield strength of the D1-T6 sample increases by 415 and 92 MPa,respectively.

Evolution of mechanical properties,localized corrosion resistance and microstructure of a high purity Al-Zn-Mg-Cu alloy during non-isothermal aging

The evolution of mechanical properties,localized corrosion resistance of a high purity Al-Zn-Mg-Cu alloy during non-isothermal aging(NIA)was investigated by hardness test,electrical conductivity test,tensile test,intergranular corrosion test,exfoliation corrosion test,slow strain rate tensile test and electrochemical test,and the mechanism has been discussed based on microstructure examination by optical microscopy,electron back scattered diffraction,scanning electron microscopy and scanning transmission electron microscopy.The NIA treatment includes a heating stage from 40℃to 180℃with a rate of 20℃/h and a cooling stage from 180℃to 40℃with a rate of 10℃/h.The results show that the hardness and strength increase rapidly during the heating stage of NIA since the increasing temperature favors the nucleation and the growth of strengthening precipitates and promotes the transformation of Guinier-Preston(GPI)zones toη'phase.During the cooling stage,the sizes ofη'phase increase with a little change in the number density,leading to a further slight increase of the hardness and strength.As NIA proceeds,the corroded morphology in the alloy changes from a layering feature to a wavy feature,the maximum corrosion depth decreases,and the reason has been analyzed based on the microstructural and microchemical feature of precipitates at grain boundaries and subgrain boundaries.

Crack elimination and strength enhancement mechanisms of selective laser melted Si-modified Al−Mn−Mg−Er−Zr alloy

In order to increase the processability and process window of the selective laser melting(SLM)-fabricated Al−Mn−Mg−Er−Zr alloy,a novel Si-modified Al−Mn−Mg−Er−Zr alloy was designed.The effect of Si alloying on the surface quality,processability,microstructure,and mechanical properties of the SLM-fabricated alloy was studied.The results showed that introducing Si into the Al−Mn−Mg−Er−Zr alloy prevented balling and keyhole formation,refined the grain size,and reduced the solidification temperature,which eliminated cracks and increased the processability and process window of the alloy.The maximum relative density of the SLM-fabricated Si/Al−Mn−Mg−Er−Zr alloy reached 99.6%.The yield strength and ultimate tensile strength of the alloy were(371±7)MPa and(518±6)MPa,respectively.These values were higher than those of the SLM-fabricated Al−Mn−Mg−Er−Zr and other Sc-free Al−Mg-based alloys.

Er在Al-Mg-Mn-Zr-Er合金中的存在形式与析出特征

利用扫描电镜、透射电镜等分析测试手段,研究了Er在Al-4.7Mg-0.7Mn-0.1Zr-0.3Er合金铸态、均匀化态以及冷轧板中的存在形式及析出特征。结果表明,Er在非平衡凝固条件下部分固溶到基体α-Al中,大部分形成初生Al3Er相断续或连续分布在晶界上,Er容易与Mn、Fe元素发生偏聚,但是很难形成Er-Mn金属间化合物;固溶的Er在均匀化退火过程中以次生Al3Er相形式析出;而沿晶界分布的Al3Er相在随后的热处理过程中并不发生分解回溶,它们在热轧、冷轧过程中破碎;冷轧板中的次生Al3Er相与基体保持良好的共格、半共格关系,可以成为合金中有效的强化相。

Microstructures and mechanical properties of Mg-Al-Sm series heat-resistant magnesium alloys

The microstructures and phase compositions of the as-cast and die-cast Mg-6.02Al-1.03 Sm, Mg-6.05Al-0.98Sm-0.56 Bi and Mg-5.95Al-1.01Sm-0.57 Zn alloys were investigated. Meanwhile, the tensile mechanical and flow properties were tested. The results show that the as-cast microstructure of Mg-6.02Al-1.03 Sm alloy is composed of δ-Mg matrix, discontinuous δ-Mg17Al12 phase and small block Al2 Sm phase with high thermal stability. Rod Mg3Bi2 phase precipitates when Bi is added, while the added metal Zn dissolves into δ-Mg matrix and δ-Mg17Al12 phase. The as-cast alloys exhibit the excellent tensile mechanical property. The tensile strength（δb） and elongation（δ） can reach 205-235 MPa and 8.5%-16.0% at ambient temperature, respectively. Meanwhile, they can also exceed 160 MPa and 14.0% at 423 K, respectively. The die-cast microstructures are refined obviously, and meanwhile the broken second phases distribute dispersedly. The die-cast alloys exhibit better tensile mechanical properties with the values of δb and δ of 240-285 MPa and 8.5%-16.5% at ambient temperature, respectively, and excellent flow property with the flow length of 1870-2420 mm. The die-cast tensile fractures at ambient temperature exhibit a typical character of ductile fracture.

Corrosion mechanism associated with Mg_2Si and Si particles in Al-Mg-Si alloys

The electrochemical behaviors and coupling behaviors of the Mg2Si and Si phases with α（Al） were investigated, the corrosion morphologies of Al alloys containing Mg2Si and Si particles were observed, and the corrosion mechanism associated with them in Al-Mg-Si alloys was advanced. The results show that Si particle is always cathodic to the alloy base, Mg2Si is anodic to the alloy base and corrosion occurs on its surface at the beginning. However, during its corrosion process, the preferential dissolution of Mg and the enrichment of Si make Mg2Si transform to cathode from anode, leading to the anodic dissolution and corrosion of the alloy base at its adjacent periphery at a later stage. As the mole ratio of Mg to Si in an Al-Mg-Si alloy is less than 1.73, it contains Mg2Si and Si particles simultaneously in the grain boundary area, and corrosion initiates on the Mg2Si surface and the precipitate-free zone （PFZ） at the adjacent periphery of Si particle. As corrosion time is extended, Si particle leads to severe anodic dissolution and corrosion of the PFZ at its adjacent periphery, expedites the polarity transformation between Mg2Si and the PFZ and accelerates the corrosion of PFZ at the adjacent periphery of Mg2Si particle.

Effect of Sr addition on microstructure of as-cast Mg-Al-Ca alloy

The microstructure evolution of Mg-Al-Ca alloys modified by the addition of strontium was investigated. It was found that Sr addition leads to the coarsening of α-Mg matrix. However, with the Sr content increasing from 0.1% to 0.5%, the grain size decreases from 83.9 to 65.8 μm. The addition of Sr ranging from 0.1% to 0.3% refines the Al2Ca phase. It changes the morphology of the Al2Ca phase from bone-shaped to granular or banding, and increases its volume fraction. The decrease of grain size of the α-Mg matrix is due to the increase of the effective undercooling degree of the melt and the constitutional undercooling in a diffusion layer ahead of the advancing solid/liquid interface in the alloy modified by the Sr additions. The modification mechanism of Al2Ca is attributed to the adsorption of Sr additions to the Al2Ca crystal. When the Sr content increases to 0.5%, the alloy is over-modified.

First principles investigation of binary intermetallics in Mg-Al-Ca-Sn alloy:Stability,electronic structures,elastic properties and thermodynamic properties

The structural stability, electronic structures, elastic properties and thermodynamic properties of the main binary phases Mg_（17）Al_（12）, Al_2Ca, Mg_2 Sn and Mg_2 Ca in Mg-Al-Ca-Sn alloy were determined from the first-principles calculation. The calculated lattice parameters are in good agreement with the experimental and literature values. The calculated heats of formation and cohesive energies show that Al_2Ca has the strongest alloying ability and structural stability. The densities of states（DOS）, Mulliken electron occupation number, metallicity and charge density difference of these compounds are given. The elastic constants of Mg_（17）Al_（12）, Al_2Ca, Mg_2 Sn and Mg_2 Ca phases are calculated, and the bulk moduli, shear moduli, elastic moduli and Poisson ratio are derived. The calculations of thermodynamic properties show that the Gibbs free energies of Al_2Ca and Mg_2 Sn are lower than that of Mg_（17）Al_（12）, which indicates that Al_2Ca and Mg_2 Sn are more stable than Mg_（17）Al_（12） phase. Hence, the heat resistance of Mg-Al-based alloys can be improved by adding Ca and Sn additions.

Influence of quench-induced precipitation on aging behavior of Al-Zn-Mg-Cu alloy

The effects of quenching and aging （T6, T7 and RRA） on the microstructural evolution of an A1-Zn-Mg-Cu alloy were investigated by hardness test, optical microscopy （OM）, transmission electron microscopy （TEM） and differential scanning calorimetry （DSC） measurements. It is found that the hardness of T6 aged sample after water-quenching is the highest. The quench sensitivities of T7 and RRA are almost the same, which are 1.2% higher than that of T6. TEM observation shows that the quench sensitivity for the studied alloy is mainly caused by heterogeneous precipitation during slow quenching. Many r/phases precipitate on A13Zr dispersoids inside recrystallized grains and at （sub） grain boundaries, while T and S phases form in the substructure with high density of dislocations and defects. After aging, the η＇ precipitates are coarser in the vicinity of equilibrium r/phase. However, the size and morphology of the precipitates show different characteristics among T6, T7 and RRA treatments. The DSC results are highly consistent with the TEM observation. The DSC curves of T6 aged samples are different from those of T7 and RRA aged samples, which also reflects the differences on the microstructure.

Microstructure,mechanical properties and creep resistance of Mg-(8%-12%)Zn-(2%-6%) Al alloys

The microstructural characteristics, mechanical properties and creep resistance of Mg-（8%-12%） Zn-（2%-6%） A1 alloys were investigated to get a better overall understanding of these series alloys. The results indicate that the microstructure of the alloys ZA82, ZA102 and ZA122 with the mass ratio of Zn to A1 of 4-6 is mainly composed of a-Mg matrix and two different morphologies of precipitates （block τ-Mg32（Al, Zn）49 and dense lamellar ε-Mg51Zn20）, the alloys ZA84, ZA104 and ZA124 with the mass ratio of 2-3 contain α-Mg matrix and only block r phases, and the alloys ZA86, ZA106 and ZA126 with the mass ratio of 1-2 consist of a-Mg matrix, block r precipitates, lamellar Ф-Al2Mg5Zn2 eutectics and flocculent β-Mg17Al12 compounds. The alloys studied with the mass ratio of Zn to A1 of 2-3 exhibit high creep resistance, and the alloy ZA124 with the continuous network of r precipitating along grain boundaries shows the highest creep resistance.

Morphology modification of Mg_2Si by Sr addition in Mg-4%Si alloy

A modification of Mg2Si in the hypereutectic Mg-4%Si alloy（mass fraction） with Sr was investigated.Two types of Mg2Si in the alloys were found：polygonal primary Mg2Si and Chinese script type eutectic Mg2Si.Adding Al-10% Sr master alloy to the Mg-4%Si alloy clearly reduced the average size of primary Mg2Si and changed the morphology of eutectic Mg2Si from Chinese script type to polyhedral or fine fibre shape.The refinement of primary Mg2Si is mainly attributed to the heterogeneous nucleation mechanism induced by the Sr-rich particles.The modification of eutectic Mg2Si results from the dissolved Sr,which alters the preferred growth manner of the eutectic.

Effects of isothermal process parameters on semisolid microstructure of Mg-8%Al-1%Si alloy

A Mg-8%Al-1%Si alloy with semisolid microstructure was fabricated by isothermal heat treatment process. The effects of isothermal process parameters such as holding temperature and holding time on the microstructure of Mg-8%Al-1%Si alloy were investigated. The results show that a non-dendritic microstructure could be obtained by isothermal heat treatment. With increasing holding temperature from 560 to 575 °C or holding time from 5 to 30 min, the liquid volume fraction increases, the average size of α-Mg grains grows larger and globular tendency becomes more obvious. In addition, the Mg2Si phase transforms from Chinese script shape to granule shape. The morphology modification mechanisium of Mg2Si phase in Mg-8%Al-1%Si alloy during the semisolid isothermal heat treatment was also studied.

Production of Mg-Al-Zn magnesium alloy sheets with ultrafine-grain microstructure by accumulative roll-bonding

Accumulative roll-bonding （ARB） was applied to Mg-Al-Zn magnesium alloy sheets to prepare ultrafine-grain microstructure. Significant grain refinement is achieved after three cycles of ARB with average grain size of about 1.3 μm. The microstructure is characterized by nearly uniform ultrafine equiaxed microstructure without twins. The evolution of the misorientation distribution during ARB was measured by EBSD. Grain refinement can be contributed to the grain subdivision induced by severe accumulated strain, the accumulated strain enhanced concurrent dynamic recovery and recrystallization as well as the complicated distribution of interface and shear strain during ARB.

Microstructure of Al-Zn-Mg-Cu-Zr-0.5Er alloy under as-cast and homogenization conditions

The billets of Al-Zn-Mg-Cu-Zr and Al-Zn-Mg-Cu-Zr-0.5Er alloys were prepared by semi-continuous direct chill casting （DCC）.The effects of trace Er on microstructure of Al-Zn-Mg-Cu-Zr alloy under as-cast and homogenization conditions were studied.The results show that the grain morphology is large dendritic structure and the grain size increases obviously by the addition of 0.5% Er.Moreover,most of Er element in the alloy segregates at grain boundary during solidification,resulting in ternary Al8Cu4Er phase.After homogenization,most of the MgZn2 phase at grain boundary has dissolved back to Al matrix in the two alloys.In the Er-containing alloy,the dissolution temperature of Al8Cu4Er phase is about 575 °C.Therefore,the homogenization treatment cannot eliminate Al8Cu4Er phase validity.

Precipitation behavior and properties of a new high strength Al-Zn-Mg-Cu alloy

The microstructure and the associated hardness, strength and electrical conductivity of a new Al-Zn-Mg-Cu alloy during one-step ageing treatment were systematically studied. The results show that the electrical conductivity of the alloy increased continuously with increasing ageing temperature and ageing time. At the early stage of ageing, the hardness and strength of the alloy increased rapidly and then reached the peak value. When aged at 120 °C, the hardness and strength maintained at high level for a long time after the peak value. The main precipitations are GPI zones, GPII zones and metastable η′ phase. GPI and GPII zones are found in the alloy after ageing for 24 h at 120 °C, which indicates that some stable GP zones can exist through the ageing process. When aged at 160 °C, the hardness and strength decreased rapidly after the peak value. The precipitation process is significantly promoted compared with that aged at 120 °C. Both GPI zones and GPII zones disappeared after ageing for 1 h at 160 °C. The main precipitates are η′ phase when aged at 160 °C for 1 h. The main precipitates are η phase when the ageing time prolongs to 24 h.

Effect of minor Zr and Sc on microstructures and mechanical properties of Al-Mg-Si-Cu-Cr-V alloys

The effects of minor contents of Zr and Sc on the microstructures and mechanical properties of Al-Mg-Si-Cu-Cr-V alloy were studied. The results show that the effects of minor Zr and Sc on the as-cast grain refinement in the ingots, the improvement in the strength of the as-extruded alloys and the restriction of high angle grain boundaries in the aged alloys can be sorted as Al3ScAl3 （Zr,Sc）Al3Zr. None of them could stop the nucleation of recrystallization, but Al3 （Zr,Sc） phase is a more effective inhibitor of dislocation movement compared to Al3 Sc in the aged alloys. Compared with the mechanical properties of the aged alloy added only 0.15% Sc, the joint addition of Zr and Sc to the alloy leads to a very slight decrease in strength with even no cost of ductility. Taking both the production cost and the little bad influence on mechanical properties into consideration, an optimal content of Zr and Sc in the Al-Mg-Si-Cu-Cr-V alloy to substitute 0.15% Sc is 0.13% Zr＋0.03% Sc.

Effects of high temperature pre-straining on natural aging and bake hardening response of Al-Mg-Si alloys

The influences of high temperature pre-straining (HT-PS) on the natural aging and bake hardening of Al?Mg?Si alloys were investigated by Vickers microhardness measurements, differential scanning calorimetry (DSC) analysis and transmission electron microscopy (TEM) characterization. The results show that pre-straining at 170 °C immediately after quenching can effectively resolve the rather high T4 temper hardness caused by the conventional room temperature (RT) pre-straining treatment, and give a better bake hardening response (BHR) after paint-bake cycle. HT-PS 7% at 170 °C for 10 min is chosen as the optimum process as it provides lower T4 temper hardness and better BHR. The simultaneous introduction of dislocations and Cluster (2) can significantly suppress the natural aging and promote the precipitation of β″ phase, and reduce the effects of deformation hardening by dynamic recovery.

Microstructural evolution of Al-0.66Mg-0.85Si alloy during homogenization

The microstructural evolution of Al-0.66Mg-0.85Si alloy was investigated by optical microscopy （OM）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and differential scanning calorimetry （DSC）. The as-cast microstructure is typical dendritical structure, consisting of α（Al）, Al（FeMn）Si, Mg2Si, AlCuMgSi and Si phases. The electron diffraction analyses indicate that the Al（FeMn）Si phase is Al15（FeMn）3Si2 and the AlCuMgSi phase is Q（Al1.9CuMg4.1Si3.3）. There are two kinds of Mg2Si phases in the as-cast microstructure. One is formed in the casting process, and the other is formed in the cooling process after casting process is finished. The phases have different crystal structures. After homogenization treatment at 545 ℃ for 20 h, Mg2Si, Si and Q intermetallic compounds are dissolved into matrix completely, and the remaining phases are α（Al） and Al15（FeMn）3Si2. The size of Al15（FeMn）3Si2 phase is decreased, and the phase is spheroidized and distributes along grain boundary discontinuously. The Zn-containing phases are not found during solidification and homogenization process.

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.

Comparison of FSW and TIG welded joints in Al-Mg-Mn-Sc-Zr alloy plates

In order to study the welding process,microstructure and properties of Al-Mg-Mn-Sc-Zr alloy,comparative methods of friction stir welding（FSW） and tungsten inert gas（TIG） were applied to the two conditions of this alloy,namely hot rolled plate and cold rolled-annealed plate.The relationships between microstructures and properties of the welded joints were investigated by means of optical microscopy and transmission electron microscopy.Compared with the base metal,the strength of FSW and TIG welded joints decreased,and the FSW welding coefficients were higher than the TIG welding coefficients.The loss of substructure strengthening and a very little loss of precipitation strengthening of Al3（Sc,Zr） cause the decreased strength of FSW welded joint.But for the TIG welded joint,the disappearance of both the strain hardening and most precipitation strengthening effect of Al3（Sc,Zr） particles contributed to its softening.At the same time,the grains in weld nugget zone of FSW welded joints were finer than those in the molten zone of TIG welded joints.