Xiaowu HU
,
Fanrong AI
,
Hong YAN
金属学报(英文版)
This paper investigated the influences of pouring temperature and cooling rate on the microstructure development and mechanical properties for casting Al-Si-Cu aluminum alloy. The microstructure of the as-cast samples was characterized by an optical microscope. The results showed that the dendrite arm spacing (DAS, λ) is well refined by pouring at a higher temperature. The λ decreases with increasing pouring temperature due to the multiplication of the nucleation sites in the superheating liquid melt, and the mechanical properties, such as microhardness and ultimate tensile strength increase correspondingly, while the elongation decreases. The relationships between microhardness and λ for the samples cooled in metal mould and sand mould, are given as HV=118.9 - 1.246 λ and HV=115.2 - 1.029 λ, respectively. The effects of the cooling rate controlled by using permanent mould casting and sand mould casing processes (the cooling medium is air and sand, respectively) on the dendrite arm spacing and mechanical properties are similar to the effect of the pouring temperature.
关键词:
Pouring temperature
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Renguo GUAN
,
Zhanyong ZHAO
,
Runze CHAO
,
Hongqian HUANG
,
Chunming LIU
金属学报(英文版)
Heat transfer of flow melt and grain refining mechanism during melt treatment by the cooling sloping plate were investigated. The results show that the cooling sloping plate can refine not only grains of alloys but also can obviously refine pure metal. Cooling ability of the plate is the key factor that induces grain refining, the plate material and the flow amount can affect cooling rate of the melt and thus affect refining effectiveness. The cooling rate of the melt on the cooling sloping plate is much faster than that of the conventional casting process, which can reach 1000 K/s and belongs to meta-rapid solidification scope. The thickness of the temperature boundary layer is much larger than that of the velocity boundary layer on the sloping plate, but the temperature gradient is small in the temperature boundary layer. Under strong cooling action by the cooling plate, most parts of the melt on the plate surface can form undercooling, which causes continuous eruptive nucleation, this is the main grain refining mechanism, and the heterogeneous nucleation on the plate surface is a helpful supplement for the nucleation.
关键词:
Grain refining
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方华
,
徐克西
,
左鹏翔
,
连博文
,
曹越
,
胡顺波
低温物理学报
在前期的研究中曾通过Ag掺杂降低Sm123／Sm211体系熔点，利用Nd123冷籽晶技术成功制备出具有理想织构的SmBCO／Ag单畴块材．但在实验结果中发现相比于未掺杂坯体，掺入As后的SmBCO坯体生长速率下降，在所考察的慢冷温区里，生长速率呈不断减小趋势，最终因自发成核而无法继续生长，使得SmBCO单畴区域局限于15×15mm。范围内．为了抑制单畴生长中的自发成核现象，本文研究了降温速率对SmBCO／Ag单畴自发成核的影响．在两组不同条件下的降温速率实验中发现，不同的降温速率对体系自发成核的抑制效果是不同的．利用降低降温速率，成功地将掺AgSmBCO单畴面积从15×15mm2增大至26×26mm2．
关键词:
SmBCO/Ag单畴
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自发成核
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降温速率
