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.

Microstructure of spray formed Al-Zn-Mg-Cu alloy with Mn addition

With the aim to improve the strength of Al-Zn-Mg-Cu alloy,the alloy billet containing Mn was produced by spray forming method,and the microstructural features were investigated using X-ray diffraction（XRD）,optical microscopy（OM）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM） and differential scanning calorimetry（DSC）.The results show that the billet mainly consists of fine equiaxial grains of MgZn2 and Al6Mn with size ranging from 5 μm to 25 μm.Nano-scaled MgZn2 is dispersed in the as-sprayed alloy,primary Al6Mn particles are precipitated at grain boundaries with an average size of 5 μm.A few CuAl2,Al3Zr and eutectic are also found in as-sprayed Al alloy.The volume fraction of the porosity is about 12%.DSC result indicates that most of the solutes are precipitated during spray forming process,and no obviously thermal effects occur below 450 ℃.Both matrix grains and Al6Mn particles grow monotonously with the increase of annealing temperature,but the growth rate of Al6Mn particles is markedly lower than that of Al grains,and the matrix grains grow rapidly when the annealing temperature is above 375 ℃.

MICROSTRUCTURAL CHARACTERISTICS AND MECHANICAL PROPERTIES OF SPRAY FORMED HIGH SPEED STEEL FOR WORK ROLL

The mechanical properties and microstructure characteristics of a high speed steel (HSS) for roll has been studied. As compared with the as-cast HSS, the spray-formed HSS have fine grain and segregation free microstructures. Carbides distribute uniformly. The morphology and types of the carbides in spray-formed HSS are different from those in as-cast HSS. The results of the high temperature tensile experiment show that, as to spray-formed HSS, there is a possibility of superplastic deformation in the range of 780-810℃.

Isothermal grain growth of reactive spray formed 7075 alloys in semi-solid state

The grain growth behavior in reactive spray formed 7075+2.91 vol percent TiCAl alloy was studied and compared with that of spray formed 7075 Al alloy at semi-solid state. Theeffects of in-situ TiC particles on the microstructure of spray formed 7075 Al alloy were alsoinvestigated. The specimens were heat-treated isothermally at various temperatures between thesolidus and liquidus of 7075 Al alloy for times in the range of 10-60 min, then quenched in water.The microstructure of reheated specimens was characterized using scanning electron microscopy andoptical microscopy. The grain size was measured using a mean linear intercept method. Results showthat the in-situ TiC particles can effectively retard grain growth and refine the grain at a limitedsize. The grain growth exponent in Arrhenius equation increases from 2 to 3, which indicates thatthe in-situ TiC particles have the significant pinning effect on grain coarsening in the semi-solidstate.

Research on flow stress of spray formed 70Si30Al alloy under hot compression deformation

The flow stress of spray formed 70Si30Al alloy was studied by hot compression on a Gleeble- 1500 test machine. The experimental results indicated that the flow stress depends on the strain rate and the deformation temperature. The flow stress increases with an increase in strain rate at a given deformation temperature. The flow stress decreases with the deformation temperature increasing at a given strain rate. The relational expression among the flow stress, the swain rate, and the deformation temperature satisfies the Arrhenius equation. The deformation activation energy of 70Si30Al alloy during hot deformation is 866.27 kJ/mol from the Arrhenius equation.

Effect of P/M value on the preforms and microstructures of spray formed 70Si30Al alloy

A novel 70Si30Al alloy was prepared by the spray forming process for electronic packaging materials. The effect of the ratio of atomization pressure to metal melt mass flux rate （P/M） on the preforms and microstructures of the spray-deposited 70Si30Al alloy was studied. The results indicate that the PIM value has a considerable influence on the formation of the preforms and the optimal value is in the range of 0.209-0.231 MPa/（kg.min^-1）. The microstructure of the spray formed 70Si30AI alloy is fine and homogenous. The primary silicon phases distributing in the aluminum matrix evenly are fine and irregular. The aluminum matrix is divided into two groups： supersaturated α-Al phase or α-Al phase and Al-Si pseudoeutectic phase or Al-Si eutectic phase.

Deformation mechanism of the spray formed 70Si30Al alloy during hot compression

The deformation mechanism of the spray formed 70Si30Al alloy was studied by hot compression on a Gleeble-1500 test machine. It is shown that hot deformation of the spray formed 70Si30Al alloy is achieved by liquid flow due to isostatic pressure and movement of solid particles due to shear force. Deformation condition depends on the nucleation rate and closure rate of the cavities. The flow stress slightly varies when the difference between the nucleation rate and closure rate of the cavities is small; however, it decreases when the nucleation rate of the cavities is greater than the closure rate of the cavities.

Microstructure of the spray formed Vanadis4 cold work die steel and its evolution during hot rolling and heat treatment

A high alloyed Vanadis4 （V4） steel was produced by spray forming process in Baosteel, and the microstructure of the as-sprayed steel and its evolution during hot rolling and annealing processes were characterized. It was found that the as-sprayed V4 steel has a homogeneous and fine scale rrficrostructure with uniform dispersion of carbides. The hot rolling temperature is the key factor in controlling the evolution of type, morphology and distribution of carbides, as well as the matrix microstructure of the as-rolled steels. The optimized processing parameters for the as-sprayed V4 steel are rolling at 1050℃ and then annealing at 900℃. The microstructural evolution mechanisms during hot rolling and annealing are determined according to the microstructural analyasis of the material at different stages.

Effect of Retrogression and Reaging on Stress Corrosion Cracking of Spray Formed Al Alloy

Stress corrosion cracking (SCC) resistance of a spray formed Al-Zn-Mg-Cu alloy underwent retrogression and reaging (RRA) was studied by slow strain rate tests in dry air and 3.5 wt% NaCl solution. The results showed that after RRA treatment, interrupted η phases at grain boundaries and slightly wide precipitate free zones could decrease SCC susceptibility of the alloy. Lots of reticular dislocations appeared in deformation process could prevent hydrogen induced cracking, and then SCC. Abundance transgranular dispersive η' phases separated out again promoted tensile strength to 759.4 MPa. The fracture ways of the specimens were dimple fracture in dry air and sub-cleavage fracture in 3.5% NaCl solution.

Strength and elongation of spray formed Al–Si–Pb alloys

The strength and elongation to fracture of spray deposited Al-Si-Pb alloys were studied as a function of lead content, silicon content, and distance from the centre to periphery of the deposit. It is found that the ultimate tensile strength, proof stress and elongation to fracture decrease, linearly and exponentially, with the increase in lead content and porosity of the deposit, respectively. Both the strengths and elongation to fracture linearly increase with increasing distance from the centre to periphery of the deposit. The ultimate tensile strength and proof stress are higher at a higher silicon content and they have a linear relationship with the hardness of the deposit.

SPRAY FORMED NICKEL-BASE SUPERALLOYS

In this paper,part of the research and development work in the field of spray formed superalloys at BIAM of China is briefly summarized. With an experimental spray forming facility,whose melting capacity is suitable for making disk and columnar shaped integral-dense and clean Ni-base superalloy preforms with low oxygen content,fine grain, uniform chemistry and improved forgeability, a series of Ni-base superalloys have been spray atomized and deposited, among which three alloys have been chosen for microstructural and mechanical properties evaluation.

Investigation into microstructure of spray formed V4 cold working mould steel and its roiling and annealing

The material selected for this work was the spray formed Vanadis4 high alloy cold working mould steel （abbreviated to V4 steel）. Its microstructure, hot rolling process, and annealing treatment have been investigated. Observed from the optical and electron microscopes, the as-sprayed V4 steel had the finer microstructure of uniform and equiaxial grains ,while after hot rolling for densification and spheroidized annealing, the V4 steel obtained an excellent spheroidized structure that is favorable to subsequent quenching and tempering treatment. The spheroidized structure and level of annealed hardness of the V4 steel are almost the same as expensive imported powder metallurgy the V4 steel. It is difficult to produce V4 steel with the conventional ingot metallurgical technique, so the multi-step and high-cost powder metallurgy method is generally used at present. Compared to the powder metallurgy technique, using the spray forming technique to produce the V4 steel has obvious advantages and potential market competitiveness in reducing production costs, simplifying working process, and shortening the production cycle.

Effect of TiB_2 addition on microstructure of spray-formed Si-30Al composite

An in situ reaction and spray forming technique were employed in the synthesis of 2% TiB2/Si-30Al composite.The formation mechanism of TiB2 particulates was explained based on thermodynamic theory.The modification of the primary Si in the Si-30Al alloy was interpreted in the light of the knowledge of atomic diffusion.The experimental results show that adding 2% TiB2 to the Si-30Al alloy can effectively refine the primary Si.Moreover,the coarsening and growth of primary Si phase in its semi-solid state was retarded effectively due to the existence of the TiB2 particulates.

Microstructure evolution of spray-formed hypereutectic Al-Si alloys in semisolid reheating process

The Al-27%Si alloy was prepared by the spray forming process,and its microstructure evolution during the semisolid reheating process was investigated.The results show that,the primary Si phase coarsens during the reheating process and the coarsening rate increases with the increase of reheating temperature.The eutectic phase is produced in the molten region when quenched in the cold water.The microstructure evolution in the semisolid state can be divided into three stages.The remarkable characteristic of the first stage is only a solid-state phase transformation process.However,the region around the α（Al） matrix gradually melts in the second stage.The primary Si in the liquid phase coarsens obviously,and the eutectic phase is produced in the molten region when the specimens are quenched in cold water.In the last stage,the same thing as that in the second stage happens except that all the α（Al） matrixes are melted.

Microstructure evolution and phase transformation of traditional cast and spray-formed hypereutectic aluminium-silicon alloys induced by heat treatment

Microstructural evolution and phase transformation induced by different heat treatments of the hypereutectic aluminium-silicon alloy, Al-25Si-5Fe-3Cu （wt%, signed as 3C）, fabricated by traditional cast （TC） and spray forming （SF） processes, were investigated by differential scanning calorimetry （DSC） and scanning electron microscopy （SEM） combined with energy dispersive X-ray spectroscopy and X-ray diffraction techniques. The results show that A17Cu2Fe phase can be formed and transformed in TC- and SF-3C alloys between 802-813 K and 800-815 K, respectively. The transformation from β-Al5FeSi to δ-Al4FeSi2 phase via peritectic reaction can occur at around 858-870 K and 876-890 K in TC- and SF-3C alloys, respectively. The starting precipitation temperature of δ-Al4FeSi2 phase as the dominant Fe-bearing phase in the TC-3C alloy is 997 K and the exothermic peak about the peritectic transformation of δ-Al4FeSi2→β-Al5FeSi is not detected in the present DSC experiments. Also, the mechanisms of the microstructural evolution and phase transformation are discussed.

Microstructural Characterization of Spray Formed FGH4095 Superalloy During Hot Deformation

In order to study the hot workability and to optimize the processing parameters for spray formed FGH4095 superalloy, thermal compression tests for spray formed FGH4095 superalloy have been finished by using a Gleeble 1500 thermal simulated test machine at the strain rates of 0.01-10.0 s 1 and temperatures of 1 050-1 140 ℃. The effects of strain rate and deformation temperature on the true stress-true strain curves and microstructure evolution were investigated. The results show that the generation of dynamic recrystallization （DRX） depends sensitively on deformation temperature. When the temperature was lower than 1080 ~C, long and＂ narrow necklace grains were shown in the microstructure. When the temperature increased to 1 140 ℃, new recrystallization grains were genera-ted. The size and shape of X＇ precipitates in the grains have a very important effect as factors of hindering sufficient migration of dislocations on plastic deformation. The result of thermal processing map is in accord with the micro-structure observation, and the best material thermal processing temperature is above 1 128 ℃.

Microstructural evolution of spray-formed Al-11.5Zn-2.0Mg-1.6Cu alloy during hot-extrusion and heat-treatment

Al-11.5Zn-2.0Mg-1.6Cu alloy was synthesized by spray forming(SF)technique followed by hot extrusion and heat-treatment.Its microstructural evolution was investigated by scanning electron microscopy(SEM),transmission electron microscopy(TEM)with energy dispersive spectroscopy(EDS)and X-ray diffraction(XRD)in the whole process.The curve of hardness as a function of aging time was obtained at 120℃.Test results indicate that the grain morphology is equiaxed and uniform in the central region of the spray-formed billet,but fine and irregular in the bottom and top regions.Both the grain boundary and the intragranular phases are identified as MgZn_(2) intermetallics.Hot extrusion promotes the refinement of the microstructure.Grain boundary phase disappears,meanwhile,η-phase(MgZn_(2))and Al_(3)Zr particles precipitate from the matrix after extrusion.The alloy reaches its maximum hardness after being aged at 120℃for 14 h,associated with a massive precipitation of intermediateη′-phase (MgZn)in the matrix.

Effect of strain rate on microstructure and mechanical properties of spray-formed Al-Cu-Mg alloy

Transmission electron microscopy(TEM),X-ray diffraction(XRD),electron backscattered diffraction(EBSD),and tensile tests were used to study the effects of strain rates(0.1,1 and 9.1 s^(-1))on the microstructure and mechanical properties of spray-formed Al-Cu-Mg alloys during large-strain rolling at 420℃.Results show that during hot rolling,the proportion of high-angle grain boundaries(HAGBs)and the degree of dynamic recrystallization(DRX)initially increase and then decrease,whereas the average grain size and dislocation density show the opposite trend with the increase of the strain rate.In addition,the number of S′phases in the matrix decreases,and the grain boundary precipitates(GBPs)become coarser and more discontinuous as the strain rate increases.When the strain rate increases from 0.1 to 9.1 s^(-1),the tensile strength of the alloy decreases from 492.45 to 427.63 MPa,whereas the elongation initially increases from 12.1%to 21.8%and then decreases to 17.7%.

Microstructure evolution and strengthening mechanisms of spray-formed 5A12 Al alloy processed by high reduction rolling

The extrusion preform of the spray-formed5A12Al alloy was hot rolled using high reduction rolling technology.By means of transmission electron microscopy(TEM),electron backscatter diffraction(EBSD)and energy dispersive spectroscopy(EDS),the microstructure evolution was studied and the strengthening and toughening mechanism was thereby proposed.The results indicate that discontinuous and continuous dynamic recrystallization occurred during the hot rolling deformation of the spray-formed5A12Al alloy.The grain size was significantly refined and the micro-scale grains formed.Partial dynamic recrystallization leads to a significant increase of dislocation density and cellular structure.The Mg atoms were distributed in the Al matrix mainly in the presence of solid solution rather than the formation of precipitate.High solid solution of Mg atoms not only hindered the dislocation motion and increased the density of dislocation,but also exhibited a remarkable solid solution strengthening effect,which contributes to the high strength and high toughness of the as-rolled sheets.The tensile strength and elongation of spray formed5A12Al alloy at room temperature after3passes hot rolling were622MPa and20%,respectively.

Structural evolution of spray-formed Al-70wt.%Si alloys during iso-thermal holding in the semi-solid state

The grain growth behavior of spray-formed Al-70wt.%Si alloys was studied in the semi-solid state. The specimens were isothermally heat-treated at various temperatures between the solidus and liquidus of Al-Si alloys and then quenched in water. The microstructure of reheated specimens was characterized using optical and scanning electron microscopies. The isothermal holding experiment was carried out to investigate grain growth behavior as a function of holding time and temperature in the semi-solid state. The coarsening mechanism and the effect of porosity on microstructure were also studied.