The microstructure and mechanical properties of as-cast A356（Al–Si） alloy castings were investigated. A356 alloy was cast into three different molds composed of sand, ferrochrome（Fe–Cr） slag, and a mixture of sa...The microstructure and mechanical properties of as-cast A356（Al–Si） alloy castings were investigated. A356 alloy was cast into three different molds composed of sand, ferrochrome（Fe–Cr） slag, and a mixture of sand and Fe–Cr. A sodium silicate–CO_2 process was used to make the necessary molds. Cylindrical-shaped castings were prepared. Cast products with no porosity and a good surface finish were achieved in all of the molds. These castings were evaluated for their metallography, secondary dendrite arm spacing（SDAS）, and mechanical properties, including hardness, compression, tensile, and impact properties. Furthermore, the tensile and impact samples were analyzed by fractography. The results show that faster heat transfer in the Fe–Cr slag molds than in either the silica sand or mixed molds led to lower SDAS values with a refined microstructure in the products cast in Fe–Cr slag molds. Consistent and enhanced mechanical properties were observed in the slag mold products than in the castings obtained from either sand or mixed molds. The fracture surface of the slag mold castings shows a dimple fracture morphology with a transgranular fracture nature. However, the fracture surfaces of the sand mold castings display brittle fracture. In conclusion, products cast in Fe–Cr slag molds exhibit an improved surface finish and enhanced mechanical properties compared to those of products cast in sand and mixed molds.展开更多
A DTM map of the study area in the Taiwan Shoal was drawn based on precise and high- density data acquired in a field survey by a multi-beam sounding system （R2Sonic2024）. We identified sand waves in the study area ...A DTM map of the study area in the Taiwan Shoal was drawn based on precise and high- density data acquired in a field survey by a multi-beam sounding system （R2Sonic2024）. We identified sand waves in the study area at water depths of 13.89-49.12 m; the main sand waves had heights of 5- 25 m, lengths of 0.1-2.0 km, and crest lines 0.1-6.5 km long. The spatial distribution of the sand waves on the seabed is dense in the north and sparse in the south and the directions range between 50°-80° and 90°-135°. Between the main sand waves, secondary sand waves develop with heights of 0.1-5.0 m and lengths of 10-100 m, which are difficult to detect by satellite remote sensing. By comparing the evolution structures of the secondary and main sand waves, we identified three evolution modes of the secondary sand waves： parallel, oblique, and divergent modes according to the relative crest directions. Suitable water depth, reciprocating current speeds between 40 and 100 cm/s, and abundant sediment supply create favorable conditions for the formation of linear sand waves. Comparing the DTM maps and profiles of the June 2012 and June 2013 surveys of the same area, we found that the shape and morphology of the sand waves remained mostly unchanged under normal hydrodynamic conditions.展开更多
基金the DST–Fly Ash unit, New Delhi, India for their financial support (Grant Ref No.FAU/DST/600(52)/2012-13)Advance Analytical laboratory, Andhra University, India for the support in SEM–EDS studies
文摘The microstructure and mechanical properties of as-cast A356（Al–Si） alloy castings were investigated. A356 alloy was cast into three different molds composed of sand, ferrochrome（Fe–Cr） slag, and a mixture of sand and Fe–Cr. A sodium silicate–CO_2 process was used to make the necessary molds. Cylindrical-shaped castings were prepared. Cast products with no porosity and a good surface finish were achieved in all of the molds. These castings were evaluated for their metallography, secondary dendrite arm spacing（SDAS）, and mechanical properties, including hardness, compression, tensile, and impact properties. Furthermore, the tensile and impact samples were analyzed by fractography. The results show that faster heat transfer in the Fe–Cr slag molds than in either the silica sand or mixed molds led to lower SDAS values with a refined microstructure in the products cast in Fe–Cr slag molds. Consistent and enhanced mechanical properties were observed in the slag mold products than in the castings obtained from either sand or mixed molds. The fracture surface of the slag mold castings shows a dimple fracture morphology with a transgranular fracture nature. However, the fracture surfaces of the sand mold castings display brittle fracture. In conclusion, products cast in Fe–Cr slag molds exhibit an improved surface finish and enhanced mechanical properties compared to those of products cast in sand and mixed molds.
基金Funding was provided by the Marine Public Special Project (201105001 and 201205004)the Natural Science Foundation (China project, 41276058)
文摘A DTM map of the study area in the Taiwan Shoal was drawn based on precise and high- density data acquired in a field survey by a multi-beam sounding system （R2Sonic2024）. We identified sand waves in the study area at water depths of 13.89-49.12 m; the main sand waves had heights of 5- 25 m, lengths of 0.1-2.0 km, and crest lines 0.1-6.5 km long. The spatial distribution of the sand waves on the seabed is dense in the north and sparse in the south and the directions range between 50°-80° and 90°-135°. Between the main sand waves, secondary sand waves develop with heights of 0.1-5.0 m and lengths of 10-100 m, which are difficult to detect by satellite remote sensing. By comparing the evolution structures of the secondary and main sand waves, we identified three evolution modes of the secondary sand waves： parallel, oblique, and divergent modes according to the relative crest directions. Suitable water depth, reciprocating current speeds between 40 and 100 cm/s, and abundant sediment supply create favorable conditions for the formation of linear sand waves. Comparing the DTM maps and profiles of the June 2012 and June 2013 surveys of the same area, we found that the shape and morphology of the sand waves remained mostly unchanged under normal hydrodynamic conditions.
