Wire-arc additive manufacture(WAAM)has great potential for manufacturing of Al-Cu components.However,inferior mechanical properties of WAAM deposited material restrict its industrial application.Inter-layer cold rolli...Wire-arc additive manufacture(WAAM)has great potential for manufacturing of Al-Cu components.However,inferior mechanical properties of WAAM deposited material restrict its industrial application.Inter-layer cold rolling and thermo-mechanical heat treatment(T8)with pre-stretching deformation between solution and aging treatment were adopted in this study.Their effects on hardness,mechanical properties and microstructure were analyzed and compared to the conventional heat treatment(T6).The results show that cold rolling increases the hardness and strengths,which further increase with T8 treatment.The ultimate tensile strength(UTS)of 513 MPa and yield stress(YS)of 413 MPa can be obtained in the inter-layer cold-rolled sample with T8 treatment,which is much higher than that in the as-deposited samples.The cold-rolled samples show higher elongation than that of as-deposited ones due to significant elimination of porosity in cold rolling;while both the T6 and T8 treatments decrease the elongation.The cold rolling and pre-stretching deformation both contribute to the formation of dense and dispersive precipitatedθ′phases,which inhibits the dislocation movement and enhances the strengths;as a result,T8 treatment shows better strengthening effect than the T6 treatment.The strengthening mechanism was analyzed and it was mainly related to work hardening and precipitation strengthening.展开更多
Facing challenges of population decline and fiscal austerity,Japan has implemented a series of initiatives to promote public-private partnerships(PPP)to ensure the sustainability of urban parks and revitalize urban sp...Facing challenges of population decline and fiscal austerity,Japan has implemented a series of initiatives to promote public-private partnerships(PPP)to ensure the sustainability of urban parks and revitalize urban spaces.These initiatives,while alleviating the government’s financial burdens on parks,have also raised concerns about the potential erosion of publicness and public interests resulted from the commercialization of public assets.This paper reviews the evolution of Japan’s urban park management system after World War II—including three phases of being purely public goods,initiating marketization,and diversifying management entities.The functions of parks have continuously enriched,and the construction,management,and operational modes have shifted from government-led towards multi-stakeholder participation,along with expanded funding sources.By examining the PPP types,driving forces,implementation mechanisms and challenges in urban park management,this paper points out that,in different eras and social contexts,the Japanese government has kept adjusting its role to maximize public interests.This has proactively updated the implications of publicness in infrastructure like urban parks,from a post-war opposite of publicness versus privateness on ownership,to the participation of private capital for a higher efficiency,and finally to a community for a stronger regional competitiveness.The reforms of urban park management system in Japan offer significant lessons and insights for urban infrastructure management in other countries and regions.展开更多
基金Project(ZZYJKT2024-08)supported by the State Key Laboratory of Precision Manufacturing for Extreme Service Performance,ChinaProject(2022JB11GX004)supported by Selection of the best Candidates to Undertake Key Research Projects by Dalian City,ChinaProject(201806835007)supported by China Scholarship Council。
文摘Wire-arc additive manufacture(WAAM)has great potential for manufacturing of Al-Cu components.However,inferior mechanical properties of WAAM deposited material restrict its industrial application.Inter-layer cold rolling and thermo-mechanical heat treatment(T8)with pre-stretching deformation between solution and aging treatment were adopted in this study.Their effects on hardness,mechanical properties and microstructure were analyzed and compared to the conventional heat treatment(T6).The results show that cold rolling increases the hardness and strengths,which further increase with T8 treatment.The ultimate tensile strength(UTS)of 513 MPa and yield stress(YS)of 413 MPa can be obtained in the inter-layer cold-rolled sample with T8 treatment,which is much higher than that in the as-deposited samples.The cold-rolled samples show higher elongation than that of as-deposited ones due to significant elimination of porosity in cold rolling;while both the T6 and T8 treatments decrease the elongation.The cold rolling and pre-stretching deformation both contribute to the formation of dense and dispersive precipitatedθ′phases,which inhibits the dislocation movement and enhances the strengths;as a result,T8 treatment shows better strengthening effect than the T6 treatment.The strengthening mechanism was analyzed and it was mainly related to work hardening and precipitation strengthening.
文摘Facing challenges of population decline and fiscal austerity,Japan has implemented a series of initiatives to promote public-private partnerships(PPP)to ensure the sustainability of urban parks and revitalize urban spaces.These initiatives,while alleviating the government’s financial burdens on parks,have also raised concerns about the potential erosion of publicness and public interests resulted from the commercialization of public assets.This paper reviews the evolution of Japan’s urban park management system after World War II—including three phases of being purely public goods,initiating marketization,and diversifying management entities.The functions of parks have continuously enriched,and the construction,management,and operational modes have shifted from government-led towards multi-stakeholder participation,along with expanded funding sources.By examining the PPP types,driving forces,implementation mechanisms and challenges in urban park management,this paper points out that,in different eras and social contexts,the Japanese government has kept adjusting its role to maximize public interests.This has proactively updated the implications of publicness in infrastructure like urban parks,from a post-war opposite of publicness versus privateness on ownership,to the participation of private capital for a higher efficiency,and finally to a community for a stronger regional competitiveness.The reforms of urban park management system in Japan offer significant lessons and insights for urban infrastructure management in other countries and regions.
