Mechanical Evaluation of AZ80 Magnesium Alloy in Cast Wrought Form

Wrought magnesium alloy AZ80 with a thick section of 20 mm was prepared by squeeze casting (SC) and permanent steel mold casting (PSMC). The porosity measurements of the SC and PSMC depicted that SC AZ80 had a pore content of 0.52%, which was 77% lower than 2.21% of PSMC AZ80 counterpart. The YS, UTS, ef, E and strengthening rate of cast AZ80 were determined by mechanical pulling. The engineering stress versus strain bended lines showed that SC AZ80 had a YS of 84.7 MPa, a UTS of 168.2 MPa, 5.1% in ef, and 25.1 GPa in modulus. But, the YS, UTS and ef of the PSMC AZ80 specimen were only 71.6 MPa, 109.0 MPa, 1.9% and 21.9 GPa. The findings of the mechanical pulling evidently depicted that the YS, UTS, ef and E of SC AZ80 were 18%, 54%, 174% and 15% higher than PSMC counterpart. The computed resilience and toughness suggested that the SC AZ80 exhibited greater resistance to tensile loads during elastic deformation and possessed higher capacity to absorb energy during plastic deformation compared to the PSMC AZ80. At the beginning of permanent change, the strengthening rate of SC AZ80 was 10,341 MPa, which was 9% greater than 9489 MPa of PSMC AZ80. The high mechanical characteristics of SC AZ80 should be primarily attributed to its low porosity level. .

Microstructure and properties of new Mg-Li-Zn wrought alloys

Cold-rolling workability, heat treatment characteristics and mechanical properties of Mg-5%-22%Li-2%Zn(mass fraction) wrought alloys were studied. Density of alloys is between 1.19 and 1.62 g/cm^3. The limit of reduction for cold rolling of the β phase alloys at 16% and 22%Li exceeds 90% at room temperature. The properties and microstructures of Mg-Li-Zn alloys were studied, which were homogenized, cold rolled, then annealed at different temperatures. Recrystallization behaviors of the alloys were investigated through microstructures observing and hardness measuring. The results show that the cast billets are suitable for rolling after homogenization at 573K for 12 h for Mg-9Li-2Zn-2Ca alloy and at 523K for 24 h for Mg-9Li-2Zn-2Ca alloy. The cold rolled plates were completely recrystallizated by annealing at 573K for 1 h.

Electroless Ni-P plating on Mg-Li alloy by two-step method

Pretreated Mg-Li alloy sheets were pre-plated in a NiCO3？2Ni（OH）2？4H2O solution to form a thin Ni-P alloy film and then plating in a NiSO4？6H2O solution was carried out to obtain a protective coating.The surface morphology,structure and corrosion resistance of the coating were studied.The results showed that a flat,bright and compact plating layer,which was integrated into the matrix metal,was obtained.The P content of the Ni-P coating reached 13.56%（mass fraction）.The hardness value of the Ni-P coating was about HV 549.The polarization curve showed that the corrosion potential of the Ni-P coating reached ？0.249 V（vs SCE）.A long passivation region was found on the polarization curve,and this phenomenon indicated that the coating has an excellent anti-corrosion property.

Deformation behavior and constitutive model for dual-phase Mg-Li alloy at elevated temperatures

In order to study the deformation behavior and evaluate the workability of the dual-phase Mg-9Li-3Al-2Sr alloy, isothermal hot compression tests were conducted using the Gleeble-3500 thermal-mechanical simulator, in ranges of elevated temperatures （423-573 K） and strain rates （0.001-1 s^-1）. Plastic instability is evident during the deformation which is in the form of serrated flow; serrated yielding is attributed to the locking of mobile dislocations by the Mg and Li atoms which diffuse during the deformation. The relationships between flow stress, strain rate and deformation temperature were analyzed and the deformation activation energy and some basic material factors at different strains were calculated using the Arrhenius equation. The effects of temperature and strain rate on deformation behavior were represented using the Zener–Hollomon parameter in an exponent-type equation. To verify the validity of the constitutive model, the predicted values and experimental flow curves under different deformation conditions were compared, the correlation coefficient （0.9970） and average absolute relative error （AARE=4.41%） were calculated. The results indicate that the constitutive model can be used to accurately predict the flow behavior of dual-phase Mg-9Li-3Al-2Sr alloy during high temperature deformation.

Microstructure and mechanical properties of Mg-Li alloy after TIG welding

Tungsten inert gas weld was carried out on super-light magnesium-lithium alloy plates with a thickness of 2 mm, using argon gas as a protecting atmosphere. The microstructure and mechanical properties of the welded joints were investigated. The results indicate that the microstructure in the fusion zone is fine, and the microstructure in the heat-affected zone is coarser than the parent metal. The tensile strength of the welded joint is about 84% that of the parent metal. The fracture occurs in a mixed type of toughness and brittleness in the heat-affected zone. During the welding process, aluminum and cerium are enriched at grain boundaries in the fusion zone.

Effect of Sr content on microstructure and mechanical properties of Mg-Li-Al-Mn alloy

The as-cast Mg-8Li-3Al-0.5Mn-xSr（LAM830-xSr, x=0-1.0） alloys were designed and prepared in a vacuum induction furnace under controlled argon atmosphere. The alloys were then processed by hot extrusion, and their microstructural evolution and mechanical properties were analyzed. Results indicate that the LAM830 alloy mainly consists of α-Mg, β-Li, Al2Mn3, and LiMgAl2 phases. Sr addition results in the precipitation of Al-Sr. Moreover, Sr addition results in a fact that the secondary dendrite arm spacing（DAS） of the primary α-Mg phase is obvious refined. Microstructure of the investigated alloys is further refined as a result of the hot extrusion treatment. The content and morphology of the secondary phases have important effects on the mechanical properties of the alloys. The as-extruded LAM830-0.5Sr alloy exhibits an optimal elongation of 22.43% and as-extruded LAM830-0.75 Sr alloy shows an optimal tensile strength of 265.46 MPa.

Recent research and developments on wrought magnesium alloys

Wrought magnesium alloys attract special interests as lightweight structural material due to their homogeneous microstructure and enhanced mechanical properties compared to as-cast alloys.In this contribution,recent research and developments on wrought magnesium alloys are reviewed from the viewpoint of the alloy design,focusing on Mg-Al,Mg-Zn and Mg-rare earth(RE)systems.The effects of different alloying elements on the microstructure and mechanical properties are described considering their strengthening mechanisms,e.g.grain refinement,precipitation and texture hardening effect.Finally,the new alloy design and also the future research of wrought magnesium alloys to improve their mechanical properties are discussed.

Key R&D activities for development of new types of wrought magnesium alloys in China

Many researchers in China are actively engaged in the development of new types of wrought magnesium alloys with low cost or with high-performances and novel plastic processing technologies.The research activities are funded primarily through four government-supported programs:the Key Technologies R&D Program of China,the National Basic Research Program of China,the National High-tech R&D Program of China,and the National Natural Science Foundation of China.The key R&D activities for the development of new wrought magnesium alloys in China are reviewed,and typical properties of some new alloys are summarized. More attentions are paid to high-strength wrought magnesium alloys and high-plasticity wrought magnesium alloys.Some novel plastic processing technologies,emerging in recent years,which aim to control deformation texture and to improve plasticity and formability especially at room temperature,are also introduced.

Influence of Rare Earth Elements on Microstructure and Mechanical Properties of Mg-Li Alloys

A series of a-based Mg-Li-A1-Zn-xRE alloys were prepared. These alloys have low density ranging from 1.5 to 1.7 g·cm^-3 and high strength properties. The influence of RE element on the microstructure and the mechanical properties of these alloys were studied. The results indicate that the addition of RE （La, Pr, Ce） leads to the formation of rodshaped intermetallic compound Al2Zn2La distributed in the matrix. Al2Zn2La induces reduction of the laminar spacing and causes refinement of the microstructure. Therefore, this compound improves the strength of alloys at a high temperature.

Mechanical properties and microstructures of a wrought AZ91 alloy

Effects of hot plastic deformation on microstructures and tensile propertiesof AZ91 alloy were investigated. Compared with as-T4 microstructures, the as-extruded samples ofAZ91 alloy with fine grains exhibit better strength and ductility due to dynamic recrystallization.The succeeded rotation forging also provides finer grains while the strength increases, but theelongation decreases. Simultaneously, wrought AZ91 alloy shows more balance properties than as-T4condition ones. An interesting elongation of 228.5% is attained in the as-extruded AZ91 alloy inspite of the coarse grains with the size of 85 μm. The two-step method enhances the superplasticproperty of AZ91 alloy. The microstructure is still keeping the same scale of grains aftersuperplastic testing.

Corrosion behavior and surface treatment of superlight Mg-Li alloys

Mg-Li alloy,as a superlight metallic engineering material,shows great potential in the fields of aerospace and militarydue to its high specific strength,better formability,and excellent electromagnetic shielding performance.The research process ofMg-Li alloys is reviewed and three main problems are pointed out.Aimed at the poor corrosion resistance of Mg-Li alloys,thecorrosion behavior is mainly summarized.The surface treatment technologies,including electroplating,electroless plating,plasmaspraying,molten salt replacement,conversion coating,anodizing,micro-arc oxidation,organic coating,and organic-inorganic hybridcoating,are introduced in detail.Finally,the future development of corrosion and protection of Mg?Li alloys is discussed.

Microstructure characteristics and solidification behavior of wrought aluminum alloy 2024 rheo-diecast with self-inoculation method

One important problem in casting wrought aluminum alloys is the high tendency to the formation of hot tears in the solidification process.By using semi-solid metal(SSM) processing,the hot tearing tendency of alloys can be minimized during casting.In the present research,the semi-solid slurry of wrought aluminum alloy 2024 was firstly prepared with a novel self-inoculation method(SIM),and then the microstructure characteristics of the semi-solid slurry and the rheo-diecastings cast with the semi-solid slurry were investigated.The results indicate that finer and more uniform globular primary α-Al particles can be obtained when the semi-solid slurry are isothermally held for a short period within the semi-solid temperature range,and the primary α-Al particles without entrapped liquid are uniformly fine,globular grains in the rheo-diecastings.The holding temperature and time affect the solid fraction,particle size,and shape factor.After the semi-solid slurry is held at 625 ℃ for 3 min and 5 min,the optimal values for the average equivalent diameter are 70.80 μm and 74.15 μm,and for the shape factor are 1.32 and 1.42,respectively.The solidification process of the rheo-diecastings is composed of the following two distinct stages:primary solidification process and secondary solidification process.The secondary solidification process consists further of the following three stages:(1) direct growth of secondary primary(α 2) phase from the surface of the primary α-Al phase particles without re-nucleation,(2) independent nucleation and growth of α 3 phase from the residual liquid,and(3) eutectic reaction at the end.

Micro-arc oxidation coatings on Mg-Li alloys

Micro-arc oxidation (MAO) method was used for the surface modification of an Mg-5wt.%Li alloy. Ceramic coatings were in-situ fabricated on the Mg-Li alloy. The morphology feature,phase composition,and corrosion-resistance of the formed ceramic coatings were studied by SEM,XRD,and electrochemical methods,respectively. The results showed that the coatings produced in a sodium silicate solution system were composed of MgO and Mg2SiO4. The ceramic coating became thicker and the content of Mg2SiO4 phase increase...

MICROSTRUCTURE MODIFICATIONS OF WROUGHT AND CAST TiAl ALLOYS

The recent advances in the microstructure modifications of wrought and cast TiAl alloys in CISRI were presented. The contributed results and discussions included the aspects and mechanisms of the refinement and homogenization of the FL microstructure in wrought TiAl alloy and the microstructure adjustment of cast TiAl alloy. The mechanical properties of the modified microstructures of wrought and cast Ti 46.5 Al 2.5 V 1.0 Cr (mole fraction,%) alloys have been experimentally evaluated as well.

Anisotropy of wrought magnesium alloys: A focused overview

In this paper, the relationship between anisotropic mechanical properties and the corresponding microstructure evolution of wrought magnesium alloys is critically reviewed. Experimental observations of the strong anisotropy(including the strength differential effect) induced by texture and twinning are discussed under different loading conditions(i.e., monotonic, cyclic and multiaxial loading). An accurate constitutive model is essential to describe the mechanical responses and to predict the forming performance considering engineering applications. Therefore, macroscale constitutive modeling of the anisotropy of magnesium alloys with directional distortional hardening are comprehensively reviewed with different approaches. To clarify the origin of the anisotropic behavior, physics-based mesoscale modeling of the anisotropy is also compared in detail.

WROUGHT TiAl ALLOY DESIGN

Empirical improvements made in cast alloys have led to gamma alloys which are a viable materials technology, and to the development of various applications for gas turbine engines, as well as automotive engines. For wrougth alloys, over the last seven years the author et al have made extensive efforts to remove their deficiencies, and to achieve an improved balance of properties, across three interrelated task areas. The first effort was directed toward understanding fundamentals, such as phase relations, microstructure evolution, and microstructure property relationships. The second task was then directed to improve the balance of properties through designing refined lamellar microstructures and microalloying. The third effort was to explore the production methods to develop desired microstructures and to optimize the alloy compositions. This paper discusses the progress made from the last two efforts.

Low-cost and high-strength Mg-Al-Ca-Zn-Mn wrought alloy with balanced ductility

A novel low-cost Mg-Al-Ca-Zn-Mn-based alloy was developed to simultaneously improve its strength and ductility.The high yield strength of 411 MPa and the high elongation to failure of~8.9%have been achieved in the as-extruded Mg-1.3Al-1.2Ca-0.5Zn-0.6Mn(wt%)sample.Microstructure characterizations showed that the high strength is mainly associated with the ultra-fined dynamically recrystallized(DRXed)grains.Moreover,high-density dislocations in the un-DRXed region and nano-precipitates are distributed among theα-Mg matrix.The high ductility property can be ascribed to the high volume fraction of DRXed grains with a much randomized texture,as well as the formations of high-density subgrains in the un-DRXed grain regions.

Solidification behavior of 6061 wrought aluminum alloy during rheo-diecasting process with self-inoculation method

The semisolid slurry of the 6061 wrought aluminum alloy was prepared by the self-inoculation method（SIM）. The effects of the isothermal holding parameters on microstructures of rheo-diecastings were investigated, and the solidification behavior of 6061 wrought aluminum alloy during the rheo-diecasting process was analyzed using OM, SEM, EDS and EBSD. The results indicate that the isothermal holding process during slurry preparation has great effect on primary α（Al） particles（α1）, but has little effect on the microstructure of secondary solidification in the process of thin-walled rheo-diecasting. Nucleation is expected to take place in the entire remaining liquid when the remaining liquid fills the die cavity, and the secondary solidification particles（α2） are formed after the process of stable growth, unstable growth and merging. The solute concentration of remaining liquid is higher than that of the original alloy due to the existence of α1 particles, hence the contents of Mg and Si in α2 particles are higher than those in α1 particles.

Rolling route for refining grains of super light Mg-Li alloys containing Sc and Be

Pioneering work on Sc or/and Be added Mg-Li alloys with refined grains was initiated. Various rolling-based thermo-mechanical treatments on these Mg-Li alloys were carried out. Four Mg-Li alloys were prepared by vacuum melting process. A unique route for producing fine grains was applied which concluded solution treatment at 350 ℃, cold rolling with 60% thickness reduction and 250 ℃ annealing, successively.

Effects of solution treatment and aging process on microstructure refining of semi-solid slurry of wrought aluminum alloy 7A09

A new method was exploited using solution treatment and aging process as a pretreatment in preparing semi-solid slurry with fine microstructure before isothermal treatment of wrought aluminum alloy 7A09.Parameters of pretreatment were optimized by orthogonal experiment design and proper precursor was prepared.The evolution of microstructure of semi-solid slurry during isothermal treatment was analyzed and the mechanism of microstructure refining was discussed.The result of orthogonal experiment design shows that the optimum parameters are 462 ℃for solution temperature,40min for solution time,132 ℃for aging temperature and 14 h for aging time.Microstructure of isothermal treatment is fine,homogenous,with globular solid grains and a solid fraction between 50%and 70%,which is qualified for later semi-solid forming process.Mechanism of microstructure evolution includes the agglomeration ofα-phase and Ostwald ripening.Precipitations prepared by solution and aging treatment prevent the grains from coarsening and promote the grain ripening to globular shape.