Aging kinetics of 14H-LPSO precipitates in Mg-Zn-Y alloy

Alloys with long-period stacking ordered structures(LPSO)have good properties and are highly regarded.Mg-Zn-Y alloy containing LPSO phase was prepared by the traditional casting method,and the aging heat treatment was performed at different temperatures and times.The microstructure and phase constitutions of the alloy were observed by means of optical microscopy and scanning electron microscopy methods.Results show the microstructure of as-cast Mg95.5Zn1.5Y3 mainly consists ofα-Mg,W phases and LPSO phases.During the aging treatment,fine lamellar-shaped 14H-LPSO phase is formed at the grain boundaries and precipitates from the supersaturated magnesium matrix,and the volume fraction increases as the aging time increases.By controlling the aging time,Mg-Zn-Y alloys with different volume fractions of 14H-LPSO phase were prepared.The aging kinetics equation of the 14H-LPSO phase is summarized,that is f=1-exp(-0.2705 t 0.6368).The phase transformation mechanism of 14H-LPSO in Mg95.5Zn1.5Y3 alloy can be described as the change of dislocation energy.     

Inluence of heat treatment on microstructure and tensile properties of a cast Al-Cu-Si-Mn alloy简

Solution and aging treatments are important approaches to improve mechanical properties and microstructure of aluminum-base alloys. In this research, a new type high strength AI-Cu-Si-Mn cast alloy was prepared. The effect of different solution and aging treatment temperatures on microstructure and mechanical properties of the AI-Cu-Si-Mn cast alloy were studied by means of microstructure observation and mechanical properties testing. Results showed that after solution treated at different temperatures for 12 h and aged at 175 ℃ for 12 h, with the increase of the solution temperature, both the tensile strength and the elongation of the alloy firstly increase and then decrease, and reach their peak values at 530 ℃. When the solution temperature is below 530 ℃, the microstructure of the alloy consists of a phase, undissolved e phase and T phase; while when it exceeds 530 ℃, the microstructure only consists of cr phase and T phase. After solution treated at 530 ℃ for 12 h and aged at different temperatures for 12 h, both the tensile strength and the elongation of the alloy firstly increase and then decrease with the increasing of temperature, and reach their peak values at 175 ℃. Therefore, the optimal heat treatment process for the alloy in this study is 12 h solution at 530 ℃ and 12 h aging at 175 ℃, and the corresponding tensile strength is 417 MPa, elongation is 4.0%.     

Effect of Thermal Treatment on the Hardness of Low Gold Content Dental Casting Ag-Pd Alloy

The age-hardening behavior and the mechanism of an experimental low gold content casting Ag-Pd alloy were studied by means of hardness test, XRD, SEM and EPMA, The results show that the hardness of specimens isothermal-aged at 400 oC after solution treated at 900 oC for 30 min increases unidirectionally from 1540 MPa to 3160 MPa with the prolongation of time. However, the hardness of the specimens isothermal-aged at 600 oC after solution treated at 900 oC for 30 min increases quickly and reaches the maximun 2870 MPa at 2 min aging time. Then the hardness decreases unidirectionally and remains at 1600-1700 MPa from 10 to 50 min aging time. Obvious precipitation takes place in the specimens isothermal-aged at 400 and 600 oC revealed by XRD. By SEM and EPMA, the precipitation particles can be seen in the specimens aged at 600 oC for 2 min after solution treated at 900 oC for 30 min. However, the time-FWMH curve shows that the increase of hardness after isothermal-aging is closely related with coherency stain from phase transformation. It is hard to define whether the phase transformation at 400 oC makes a contribution to the change of hardness     

Effects of heat treatment on characteristics of porous Ni-rich NiTi SMA prepared by SHS technique

The effects of heat treatment on the microstructure and compressive properties of porous Ni-rich NiTi shape memory alloy （SMA） fabricated by self-propagating high-temperature synthesis （SHS） were investigated. The solution treatment at 1050℃ has little effects on stable Ti2Ni second phase, however, it decreases the amount of Ni4Zi3 phase derived from the SHS process and results in the improvement of the ductility of porous NiTi SMA. The subsequent aging treatment after solution treatment could lead to the precipitation of the discrete Ni4Ti3 phase in NiTi matrix grains, which increases the brittleness of porous NiTi SMA. Porous NiTi SMA presents a composite fracture behavior consisting of a ductile fracture of NiTi matrix and a cleavage fracture of second phase particles. Many cracks existing on the interfaces indicate that the bonding of the matrix with second phase particles is weak.     

Hardening mechanism of MP159 alloy induced by aging

The microstructural changes of both solution heat treated (ST) and cold worked (CW) MP159 alloy during aging were investigated by optical microscopy and transmission electron microscopy (TEM). The results indicate that both solution heat treated (ST) and cold worked (CW) MP159 alloy could be hardened by aging. This aging induced hardening is attributable to the precipitation of a very finely dispersed ordered cubic γ‘ phase particles with only several nanometres in diameter. The hexagonal close packed (HCP) ε-martensite precipitated during aging of both CW MP159 and CW MP35N, and the hexagonal ordered Co3Mo phase of the DO19 structure type precipitated, during aging of CW MP35N,have not been found in the oresent investigation.     

Arc Erosion Behavior of Cu–0.23Be–0.84Co Alloy after Heat Treatment: An Experimental Study

The arc erosion behavior of Cu–0.23Be–0.84 Co alloy after heat treatment was investigated experimentally by a JF04 C electric contact test system. The arc duration, arc energy, contact resistance and contact pressure of Cu–0.23Be–0.84 Co alloy after solution treatment and aging treatment were analyzed. The arc erosion morphologies were contrastively observed by a three-dimensional measuring system and scanning electron microscopy. For the Cu–0.23Be–0.84 Co alloy in solution state and aging state, the maximum values of arc duration are 90 and 110 ms, and the arc energies are 15,000 and18,000 m J, respectively. The maximum value of the contact resistance of Cu–0.23Be–0.84 Co alloy in different states is about 33 m X. The contact pressure of Cu–0.23Be–0.84 Co alloy in solution state generally changes between 50 and 60 c N during whole make-and-break contacts, while in aging state, it has a larger fluctuation range. Moreover, the quality of moving contact(anode) decreases, while static contact(cathode) increases. The materials transfer from anode to cathode during make-and-break contacts. The total mass losses of Cu–0.23Be–0.84 Co alloy in solution state and aging state are 3and 1.2 mg, respectively. In addition, a number of discrete corrosion pits, molten droplet, porosity and cavity distribute on the surface of moving contact and static contact. The arc erosion model of Cu–0.23Be–0.84 Co alloy in make-and-break contact was built. The arc erosion resistance of Cu–0.23Be–0.84 Co alloy after heat treatment is closely related to the microstructure and the properties of contact materials. This experimental study is important to evaluate the anode or cathode electrocorrosion fatigue life.     

Effects of heat-treatment on microstructure of wrought magnesium alloy ZK60

The microstructure of the as-cast, as-solution-treated and as-aged wrought magnesium alloy ZK60 was studied. The results indicate that the microstructure of the as-cast ZK60 alloy is mainly composed of network eutectic （a-Mg＋MgZn） and divorced euteetic MgZn, which semi-continuously distribute along the grain boundaries or in the interdendritic area and almost dissolve into the matrix after solid solution treatment. The Laves phase MgZn2 is not sensitive to the heat treatment and seems to form at the early stage of solidification and keeps its size and shape till the aging stage. It is believed that the occurrence of the Laves phase in the ZK60 alloy would possibly contribute to the defects. Many new phases, including MgZn phase which is different from that forms during eutectic reaction, precipitate after aging treatment.     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

Effect of phosphorus and heat treatment on microstructure of Al-25%Si alloy

It is known that phosphorus can refine the primary silicon and heat treatment can spheroidize the eutectic silicon. This paper presents an optimal combination of heat treatment processes and P refinement on hypereutectic Al-Si alloy. The optimal P addition amount, and the solution and aging temperatures for Al-25%Si alloy were obtained through the orthogonal experiment, and their modification effects were discussed. The results show that P addition has the greatest modification effect, followed by aging temperature, and the modification effect of solution temperature is the least. The optimized modification parameters are: addition of 0.6% P, solution at 540 oC and aging at 160 oC . In addition, the cooling curve, superheating and hardness of the alloy were also analyzed.     

Effects of heat treatment on microstructure evolution and mechanical properties of Mg-6Zn-1.4Y-0.6Zr alloy

To investigate the effects of solution temperature and the decomposition of I-phase on the microstructure, phase composition and mechanical properties of as-cast Mg-6Zn-1.4Y-0.6Zr alloy, solution treatment at 440 oC, 460 oC and 480 oC and further aging treatment were conducted on the alloy. The results indicate that the net-like intermetallic compounds(mainly I-phase) dissolve into the α-Mg matrix gradually with the increase of solution temperature from 440 oC to 480 oC. Besides, the I-phase decomposes completely at 480 oC, with the formation of fine W-phase(thermal stable phase) and Mg_7Zn_3 phase. In addition, a great number of fine and dispersive Mg-Zn binary phases precipitate in the α-Mg matrix during the aging treatment. Due to the increase of solute atoms and the precipitation of strengthening phases, such as W-phase and Mg-Zn phases, the optimal strength is obtained after solution treatment at 460 oC for 8 h and aged at 200 oC for 16 h. The yield strength(YS), ultimate tensile strength(UTS) and elongation are 208 MPa, 257 MPa and 3.8%, respectively. Compared with the as-cast alloy, the increments of YS and UTS are 117% and 58%, respectively, while the decrement of elongation is 46%.     

Relationship between microstructure and tensile properties on a near-β titanium alloy after multidirectional forging and heat treatment

In this study, a new near-beta titanium alloy, Ti-4Al-1Sn-2Zr-5Mo-8V-2.5Cr, was prepared by induction skull melting(ISM) and multidirectional forging. The effect of aging heat treatment on microstructure and tensile properties of the alloy after solution treatment in the twophase(α + β) region was investigated. The micros tructure results show that the globular primary α phase(α_p) and the needle-like secondary α phase(α_s) are precipitated in the β matrix. The size of α_s increases with the increase in aging temperature,while the content of α_s goes up to a peak value and then decreases. The tensile testing results show that the strength increases first and then decreases with the increase in temperature. The variation of ductility presents the opposite way compared with the trend of strength level.When aged at 500 ℃, the alloy exhibits an excellent balance of tensile strength(1529 MPa) and elongation(9.22%). And the relative mechanism of strengthening and toughening was analyzed and discussed.     

The microstructure of a single crystal superalloy after different aging heat treatments

To study the influence of aging heat treatments on the microstructure of single crystal superalloys with high content of refractory elements and optimal the aging heat treatment regimes, a single crystal superalloy containing 22 wt% refractory elements was investigated.Results show that for the experimental alloy, even the homogenization-solution heat treatment for 25 h cannot homogenize the alloying elements completely. During primary aging heat treatment, γ' phase grows larger and turns to regular cubes. Higher aging temperature induces larger γ' cubes. For specimens with primary aging heat treated at 1120 ℃,γ' morphology does not change apparently during secondary aging heat treatment. For specimens with primary aging heat treatment at 1150 ℃,γ'phase in interdendrite grows obviously comparing with that in dendrites. By analyzing the precipitating kinetics of γ'phase, it is found that owning to the dendrite segregation and different aging heat treatment temperatures, γ' phase at different regions grows under the control of different factors at different aging heat treatment stages. The two controlling factors that are driving forces of phase transformation and element diffusion rate induce obviously different growth rates of γ' phase. As a result, the γ'-precipitating behaviors are variable based on different solute concentrations and aging temperatures. For advanced single crystal superalloys that are supposed to be used at relatively high temperatures, the final γ' size after aging heat treatment is suggested to be close to the crossing point of diffusion controlling curve and driving force controlling curve corresponding to the serving temperature. And then,high-temperature properties can be improved.     

Effect of Cd and Sn Addition on the Microstructure and Mechanical Properties of Al-Si-Cu-Mg Cast Alloy

The present work has investigated the effect of trace elements Cd and Sn on the microstructure and mechanical properties of Al-Si-Cu-Mg cast alloy. With the increase of Cd addition the strength of alloy rises at first and then drops. The optimal amount of Cd and Sn addition for AI-Si-Cu-Mg alloy is about 0.27% and 0.1% respectively. Due to the formation of some coarse Cd-rich phases and pure Cd particles the mechanical properties of alloy decrease when Cd amount exceeds 0.27%. When more than 0.1% Sn added, some Sn atoms form low-melting eutectic compound at grain boundary, and then cause over-burning in alloy when solution treated, which may deteriorate properties of alloy, especially ductility of alloy.On the other hand, the addition of Cd and Sn remarkably increases the peak hardness and reduces the time to reach aging peak in Al-Si-Cu-Mg alloy. The action of Cd/Sn in quaternary Al-Si-Cu-Mg alloy is effectively the same as that occur in binary Al-Cu alloy that the enhanced hardening associated with Cd/Sn addition is due to the promotion of the θ‘phase.     

Influence of Mg Contents on Aging Precipitation Behavior of AI-3.5Cu-xMg Alloy

The influence of Mg content on the microstructures and mechanical properties at room temperatures of Al-3.5Cu-(0.71-1.81)Mg alloys was studied.Precipitation phases in the alloys were identified by TEM and HRTEM.The results show that when Mg contents increase from 0.71 to 1.81 wt%,the precipitates are transformed from S,S″,Ω,and θ’ phases to Sand S′phases,and Ω phase is first observed in Al-3.48Cu-0.71 Mg alloy with Cu/Mg mass ratio of 5 during the conventional aging heat treatment(190 ℃/12 h).Regard to aging hardness effect of the tested alloys,the hardness of the alloys improves with the increase of Mg content,but the increases become slow when Mg content is greater than 1.35 wt%.     

Thermomechanical treatment of super high strength Cu-8.0Ni-1.8Si alloy

The microstructures and properties of Cu-8.0Ni-1.8Si alloy subjected to different heat treatments were examined by mechanical and electrical properties measurements, optical and transmission electron microscopes observation. The results show that the precipitation process during aging can be accelerated by the cold deforming before aging. As the Cu-8.0Ni-1.8Si alloy is subjected to solution treatment at 970 ℃ for 4 h, cold rolling to 60% reduction, and then aging at 450 ℃ for 60 min, its properties are σb=1 050 MPa, σ0.2=786 MPa, δ=3.2% and conductivity 27.9%（IACS）. The strengthening mechanisms of the alloy include spinodal decomposition strengthening, ordering strengthening and precipitation strengthening. The precipitation of the alloy is nano-scale Ni2Si phase.     

Effect of Mg on microstructures and properties of Al-Mg-Si-Cu aluminium alloys for automotive body sheets

The effects of variation of Mg content on microstructures, the tensile properties and the formability of Al-Mg-Si-Cu alloys for automotive body sheets were investigated by means of scan electron microscopy, optical metallographic analysis, tensile and Ericsson tests. The results show that for Al-Mg-Si-Cu aluminium alloys with excessive Si, with an increment of Mg content, the strength enhances, the specific elongation and Erisson values of alloys decrease, and the number of Mg2 Si constituent increases and that of AI(MnFe)Si type constituents reduces. Al-Mg-Si-Cu aluminium alloys with excessive Si for automotive body sheets can present obviously the paint bake hardenability during the paint hake cycle (i. e. artificial aging at 170℃ for 30 min immediately after the solution treatment and quenching). Suitable Mg content should be controlled in the range of 0.8% and 1.2%(mass fraction).     

Effects of trace Cr on as-cast microstructure and microstructural evolution of semi-solid isothermal heat treatment ZC61 magnesium alloy

The content and kind of trace elements in magnesium alloys have important effects on their ascast and semi-solid microstructures. In this research work, effects of trace Cr on as-cast and semi-solid microstructures of ZC61 magnesium alloy were investigated by metal mold casting and semi-solid isothermal heat treatment. The results show that the addition of Cr can refine the α-Mg phase without generating a new phase, noticeably change the eutectic phase, and decrease the average size of solid particles at the same isothermal heat treatment conditions. Non-dendritic microstructures of all alloys are constituted of α_1-Mg phases, α_2-Mg phases and eutectic phases after water quenching. With isothermal temperature increased or holding time prolonged, the eutectic microstructure(α-Mg+MgZn_2+CuMgZn) at the grain boundaries in as-cast alloy is melted preferentially and then turned into semi-solid non-dendritic microstructure by processes of initial coarsening, microstructure separation, spheroidizing and final coarsening. Especially when the ZC61-0.1 Cr alloy was treated at 585 ℃ for 30 min, the ideal non-dendritic microstructure can be obtained, and the corresponding solid particle size and shape factor were 37.5 μm and 1.33, respectively. The coarsening process of solid α-Mg phase at higher temperature or longer time, which is affected by both combining growth and Ostwald ripening mechanism, is refrained when Cr is added to the ZC61 alloy.     

Effects of aging on the microstructures and mechanical properties of extruded AM50 ＋ xCa magnesium alloys

The effects of aging treatment on the microstructures and mechanical properties of extruded AM50 ＋ xCa alloys （x=0, 1, 2 wt.%） were studied. The results indicated the secondary phase Mgl7Al12 precipitated from the saturated α-Mg solid solution while Al2Ca changed slightly when the aging time was increased. The hardness of extruded AM50 ＋ xCa al- loys increased initially to its peak, and then dropped to reach its original hardness with the increase in aging time. With the increase in aging temperature, the hardness of the AM50 ＋ 2Ca ahoy decreased, whereas the hardness of AM50 and AM50 ＋ 1Ca alloys decreased in the initial stages of aging treatment and increased in the later stages of aging treatment. The tensile strengths of AM50 and AM50 ＋ 1Ca alloys increased after aging treatment for the precipitation of Mg17Al12 phase, which increases the resistance against dislocation movement at the grain boundary; with increase in aging temperature, their tensile strengths increased. For AM50 ＋ 2Ca alloy, the tensile strength declined after aging at 150℃ and 175℃, while it increased slightly at 200℃. The ductility of AM50 ＋ xCa alloys （x = 0, 1, 2 wt.%） declined after aging treatment.