High strength Al Zn Mg Cu alloys were produced by spray forming process, and compacted by hot extrusion. The results show that the as deposited billets have fine grained microstructure and low porosity. After heat tre...High strength Al Zn Mg Cu alloys were produced by spray forming process, and compacted by hot extrusion. The results show that the as deposited billets have fine grained microstructure and low porosity. After heat treatment, mechanical properties increase greatly: tensile strength up to 754 MPa, yield strength up to 722 MPa, fracture elongation up to 8%, and elastic modulus up to 72 GPa, respectively. [展开更多
In the course of plasma spray, the plasma jet is comprehensively functioned by such effects as thermal pinch, magnetic pinch and mechanical compression and the flow is jetting at a high speed, the energy is concentrat...In the course of plasma spray, the plasma jet is comprehensively functioned by such effects as thermal pinch, magnetic pinch and mechanical compression and the flow is jetting at a high speed, the energy is concentrated and its center temperature is so high as to reach upwards of 15 000 ℃ which is capable of melting various kinds of materials inclusive of ceramic, it has a broad applied prospects in the fields of automobile, electronics, telecommunications, medical treatment, air navigation & space navigation and light industries etc because of being able to rapid fabricate thin-walled metals, ceramics and alloy parts thereof, metal moulds, functionally gradient material moulds and so on, and it has become a research spotlight for the scholars. The technology of plasma spray forming (PSF) is introduced, and the two different kinds of technique presented in this paper are studied. Some typical links in the course of technical process is also analyzed, including original prototype fabrication and surface treatment, post-treatment of formed workpiece and demoulding methods. When spraying, it should select the appropriate making methods of prototype according to the dimensions, shapes and forming accuracy as required by the formed parts. At the same time, it should be paid to the characteristic of the material for the prototype. The main purpose of surface treatment of the prototype is to raise the quality of formed parts and ensure the integrity demoulding of the coating. The method of the prototype’s surface treatment is closely related to the demoulding method, which is mainly comprised of destructive demoulding, non-destructive demoulding and composite demoulding, and is key technology in PSF. In order to eliminate these intrinsic defects and improve its performance, the fabricated parts can be given the necessary post-treatment so as to further raise the mechanical strength and surface quality. There are many methods for the post-treatment such as chemical reinforcment, metal melt-infiltration, laser-melting and self-propagating high-temperature synthesis, etc., all these methods can decrease the porosity and raise the quality of coating and service performance; whereas the finishing machining can improve the surface roughness of spray formed parts. In the course of spray forming, affected by such complex and complicated factors as electric field, the entangled ambient gas and introduced powder, as a result, it shall induce the instability of the spray condition and affect the forming quality. This paper has, on the basis of large quantity of experiments, analyzed every links in the course of PSF, summarized and evaluated the main factors affecting on the quality of formed parts, such as prototype characteristic, characteristic of plasma jet, powder characteristic, spray gun and spray parameters. The experiments prove that the process of PSF is simple and the cost is lower in rapid tooling with complex and complicated fine patterns, and PSF is apt to form special-shape and thin-walled parts made of some protective materials so as to protect those fragile workpieces. Therefore PSF is a new technology with broad and brilliant prospects of development.展开更多
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 e...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.展开更多
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 t...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.展开更多
Gas mass flux rate,metal mass flux rate and outlet gas velocity are three atomization scale parameters which greatly affect the atomization efficiency. A Laval-style annual slot supersonic nozzle is designed by optimi...Gas mass flux rate,metal mass flux rate and outlet gas velocity are three atomization scale parameters which greatly affect the atomization efficiency. A Laval-style annual slot supersonic nozzle is designed by optimizing the geometric parameters of delivery tube outlet and gas outlet to obtain applicable atomization scale parameters. A computational fluid flow model is adopted to investigate the effect of atomization gas pressure ( P0 ) on the gas flow field in gas atomization progress. The numerical results show that the outlet gas velocity of the nozzle is not affected by P0 and the maximum gas velocity reaches 452 m / s. The alternation of aspiration pressure ( ΔP) is caused by the variations of stagnation pressure and location of Mach shock disk, and hardly by the location of stagnation point. The aspiration pressure is found to decrease as P0 increases when P0 < 1. 3 MPa. However,at a higher atomization gas pressure increasing P0 causes an opposite: the aspiration pressure atomization increases with the gas pressure,and keeps a plateau when P0 > 2. 0 MPa. The minimum aspiration pressure ΔP = - 70 kPa is obtained at P0 = 1. 3 MPa. The results indicate that the designed Laval- style annual slot nozzle has well atomization characteristic at lower atomization pressure.展开更多
文摘High strength Al Zn Mg Cu alloys were produced by spray forming process, and compacted by hot extrusion. The results show that the as deposited billets have fine grained microstructure and low porosity. After heat treatment, mechanical properties increase greatly: tensile strength up to 754 MPa, yield strength up to 722 MPa, fracture elongation up to 8%, and elastic modulus up to 72 GPa, respectively. [
文摘In the course of plasma spray, the plasma jet is comprehensively functioned by such effects as thermal pinch, magnetic pinch and mechanical compression and the flow is jetting at a high speed, the energy is concentrated and its center temperature is so high as to reach upwards of 15 000 ℃ which is capable of melting various kinds of materials inclusive of ceramic, it has a broad applied prospects in the fields of automobile, electronics, telecommunications, medical treatment, air navigation & space navigation and light industries etc because of being able to rapid fabricate thin-walled metals, ceramics and alloy parts thereof, metal moulds, functionally gradient material moulds and so on, and it has become a research spotlight for the scholars. The technology of plasma spray forming (PSF) is introduced, and the two different kinds of technique presented in this paper are studied. Some typical links in the course of technical process is also analyzed, including original prototype fabrication and surface treatment, post-treatment of formed workpiece and demoulding methods. When spraying, it should select the appropriate making methods of prototype according to the dimensions, shapes and forming accuracy as required by the formed parts. At the same time, it should be paid to the characteristic of the material for the prototype. The main purpose of surface treatment of the prototype is to raise the quality of formed parts and ensure the integrity demoulding of the coating. The method of the prototype’s surface treatment is closely related to the demoulding method, which is mainly comprised of destructive demoulding, non-destructive demoulding and composite demoulding, and is key technology in PSF. In order to eliminate these intrinsic defects and improve its performance, the fabricated parts can be given the necessary post-treatment so as to further raise the mechanical strength and surface quality. There are many methods for the post-treatment such as chemical reinforcment, metal melt-infiltration, laser-melting and self-propagating high-temperature synthesis, etc., all these methods can decrease the porosity and raise the quality of coating and service performance; whereas the finishing machining can improve the surface roughness of spray formed parts. In the course of spray forming, affected by such complex and complicated factors as electric field, the entangled ambient gas and introduced powder, as a result, it shall induce the instability of the spray condition and affect the forming quality. This paper has, on the basis of large quantity of experiments, analyzed every links in the course of PSF, summarized and evaluated the main factors affecting on the quality of formed parts, such as prototype characteristic, characteristic of plasma jet, powder characteristic, spray gun and spray parameters. The experiments prove that the process of PSF is simple and the cost is lower in rapid tooling with complex and complicated fine patterns, and PSF is apt to form special-shape and thin-walled parts made of some protective materials so as to protect those fragile workpieces. Therefore PSF is a new technology with broad and brilliant prospects of development.
文摘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.
文摘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.
文摘Gas mass flux rate,metal mass flux rate and outlet gas velocity are three atomization scale parameters which greatly affect the atomization efficiency. A Laval-style annual slot supersonic nozzle is designed by optimizing the geometric parameters of delivery tube outlet and gas outlet to obtain applicable atomization scale parameters. A computational fluid flow model is adopted to investigate the effect of atomization gas pressure ( P0 ) on the gas flow field in gas atomization progress. The numerical results show that the outlet gas velocity of the nozzle is not affected by P0 and the maximum gas velocity reaches 452 m / s. The alternation of aspiration pressure ( ΔP) is caused by the variations of stagnation pressure and location of Mach shock disk, and hardly by the location of stagnation point. The aspiration pressure is found to decrease as P0 increases when P0 < 1. 3 MPa. However,at a higher atomization gas pressure increasing P0 causes an opposite: the aspiration pressure atomization increases with the gas pressure,and keeps a plateau when P0 > 2. 0 MPa. The minimum aspiration pressure ΔP = - 70 kPa is obtained at P0 = 1. 3 MPa. The results indicate that the designed Laval- style annual slot nozzle has well atomization characteristic at lower atomization pressure.
