Based on current situation of frequent occurrence of food incidents,this paper made an in-depth analysis on causes of food incidents,mainly including weak awareness of frontline staff,excessive pursuit of food produce...Based on current situation of frequent occurrence of food incidents,this paper made an in-depth analysis on causes of food incidents,mainly including weak awareness of frontline staff,excessive pursuit of food producers and operators for profit,vacancy and lagging of administrative supervision,and lack of honesty and public interests. In view of these four causes,it came up with pertinent recommendations from the perspective of improving the credit situation.展开更多
In this study,a wire oscillating laser additive manufacturing(O-WLAM)process was used to deposit 2319 aluminum alloy samples.The optimization of the deposition process parameters made it possible to obtain samples wit...In this study,a wire oscillating laser additive manufacturing(O-WLAM)process was used to deposit 2319 aluminum alloy samples.The optimization of the deposition process parameters made it possible to obtain samples with smooth surfaces and extremely low porosities.The effects of the deposition parameters on the formability and evolution of the microstructure and mechanical properties before and after heat treatment were studied.The oscillating laser deposition of 2319 aluminum alloy,especially the circular oscillation mode,significantly reduced the porosity and improved the process stability and formability compared with non-oscillating laser deposition.There were clear boundaries between the deposition units in the deposition state,the interior of which was dominated by columnar crystals with many rod-and point-shaped precipitates.After the heat treatment,theθphase was significantly dissolved.The residual dot-and rod-shapedθ'phases were dispersedly distributed,exhibiting an obvious precipitation-hardening effect.The samples in the as-deposited state had a tensile strength of 245–265 MPa,an elongation of approximately 12.6%,and an 87 HV microhardness.After heat treatment at 530°C for 20 h and aging at 175°C for 18 h,the tensile strength,elongation,and microhardness reached 425–440 MPa,approximately 10%,and 153 HV,respectively.The performance improved significantly without significant anisotropy.Compared with the samples produced by wire arc additive manufacturing(WAAM),the tensile strength increased by approximately 10%,and the strength and microhardness were significantly improved.展开更多
The TEM and HRTEM were utilized to investigate the phase transformation of hydrogenated Ti-6Al-4V alloys （0 wt pct–0.9 wt pct H） treated by annealing and quenching from β field. The results indicate that the ortho...The TEM and HRTEM were utilized to investigate the phase transformation of hydrogenated Ti-6Al-4V alloys （0 wt pct–0.9 wt pct H） treated by annealing and quenching from β field. The results indicate that the orthorhombic α martensite and β phase appear progressively with the increase of hydrogen concentration. On the other hand, hydrides with sizes of 2–5 nm are observed in the specimens containing more than 0.6 wt pct hydrogen. The formation of α and twins can be attributed to the internal stress caused by solid solution of hydrogen and hydrides precipitation.展开更多
文摘Based on current situation of frequent occurrence of food incidents,this paper made an in-depth analysis on causes of food incidents,mainly including weak awareness of frontline staff,excessive pursuit of food producers and operators for profit,vacancy and lagging of administrative supervision,and lack of honesty and public interests. In view of these four causes,it came up with pertinent recommendations from the perspective of improving the credit situation.
基金National Natural Science Foundation of China(Grant No.52175370).
文摘In this study,a wire oscillating laser additive manufacturing(O-WLAM)process was used to deposit 2319 aluminum alloy samples.The optimization of the deposition process parameters made it possible to obtain samples with smooth surfaces and extremely low porosities.The effects of the deposition parameters on the formability and evolution of the microstructure and mechanical properties before and after heat treatment were studied.The oscillating laser deposition of 2319 aluminum alloy,especially the circular oscillation mode,significantly reduced the porosity and improved the process stability and formability compared with non-oscillating laser deposition.There were clear boundaries between the deposition units in the deposition state,the interior of which was dominated by columnar crystals with many rod-and point-shaped precipitates.After the heat treatment,theθphase was significantly dissolved.The residual dot-and rod-shapedθ'phases were dispersedly distributed,exhibiting an obvious precipitation-hardening effect.The samples in the as-deposited state had a tensile strength of 245–265 MPa,an elongation of approximately 12.6%,and an 87 HV microhardness.After heat treatment at 530°C for 20 h and aging at 175°C for 18 h,the tensile strength,elongation,and microhardness reached 425–440 MPa,approximately 10%,and 153 HV,respectively.The performance improved significantly without significant anisotropy.Compared with the samples produced by wire arc additive manufacturing(WAAM),the tensile strength increased by approximately 10%,and the strength and microhardness were significantly improved.
文摘The TEM and HRTEM were utilized to investigate the phase transformation of hydrogenated Ti-6Al-4V alloys （0 wt pct–0.9 wt pct H） treated by annealing and quenching from β field. The results indicate that the orthorhombic α martensite and β phase appear progressively with the increase of hydrogen concentration. On the other hand, hydrides with sizes of 2–5 nm are observed in the specimens containing more than 0.6 wt pct hydrogen. The formation of α and twins can be attributed to the internal stress caused by solid solution of hydrogen and hydrides precipitation.
