Strengthening technology and mechanism for semi-solid die casting of aluminum alloy

Combined with theoretical evaluation,an optimized strengthening process for the semi-solid die castings of A356 aluminum alloy was obtained by studying the mechanical properties of castings solution treated and aged under different conditions in detail,then,the semi-solid die castings and liquid die castings were heat treated with the optimized process.The results show that the mechanical properties of semi-solid die castings of aluminum alloy are superior to those of the liquid die castings,especially the strengthening degree of heat treated semi-solid die castingsis much greater than that of liquid die castings with the tensile strength more than 330 MPa and the elongation more than 10％,and this is mainly contributed to the non-dendritic and more compact microstructure of semi-solid die castings.The strengthening mechanism of heat treatment for the semi-solid die castings of A356 aluminum alloy is due to the dispersive precipitation of the second phase(Mg2 Si) and formation of GP Zone.     

换热器表面预处理及防腐工艺

石化换热器许多设备都由碳钢制作,需要涂镀渗防腐,为保证防腐层质量,需要进行严格的表面预处理。概述了机械与化学表面预处理及相关的防腐工艺。     

纺牵—步法中粗旦丙纶长丝沸水收缩率初探

在纺牵联合一步法纺丝机上研究了丙纶切片的熔融指数对纤维沸水收缩率的影响，发现熔融指数高的切片，其纤维的沸水收缩率变化大。沸水收缩率随热定型的温度升高而下降。沸水收缩率可根据用户提供中心值（Ｍ）通过实验确定，一般以Ｍ±１．５为宜。     

一步法生产涤纶FDY工艺的探讨

利用ＫＶ７３１纺丝设备一步法生产出涤纶ＦＤＹ，探讨了热辊拉伸和熔体温度对纤维质量的影响。采用高特性粘数的聚酯切片，严格控制纺丝工艺，可以在５０００ｍ／ｍｉｎ的纺丝速度下纺制高质量的细旦涤纶ＦＤＹ。     

应用WCA微扰理论推算非极性液体比热容的新方法

本文首次将统计热力学的Ｗｅｅｋｓ－Ｃｈａｎｄｌｅｒ－Ａｎｄｅｒｓｏｎ（简称ＷＣＡ）微扰理论应用于非极性液体定容比热容和定压比热容的推算，用一些液体的ｐ－ｖ－Ｔ实验数据拟合了理论中所用ＬＪ势能函数的势能参数，并提出一个通用关联式。本文方法具有通用性，在编制的计算程序中只需输入物质的临界温度、临界比容、偏心因子等就能算出相应的比热容，工程应用十分方便。     

Effect of Twin-Plane Reentrant Edge on the Coarsening Behavior of Barium Titanate Grains

When BaTiO₃ ceramics were sintered at relatively low temperatures (≤1250°C), the grains with reentrant edges caused by a (111) double twin grew exclusively. As a result, a microstructure with a bimodal grain-size distribution composed of platelike large grains and fine matrix grains was obtained. In contrast, at the usual sintering temperature between 1250° and 1350°C, grains containing a (111) double twin did not exhibit any growth advantage. In this case, a coarse and uniform microstructure was obtained. When this coarse-grained specimen was further heat-treated at 1365°C, the grains possessing a double twin were observed to grow exclusively again. The results were explained in terms of a coarsening process controlled by two-dimensional nucleation.     

板壳式换热器设置膨胀节的判定

介绍板壳式换热器的主要特点和应用。当壳体与板束温差较大时,笔者通过对产品开发的生产实践,提出解决板壳式换热器要否设置膨胀节的类似判定方法。     

Air-source heat pump coupled with economized vapor injection scroll compressor and ejector:Design and experimental research

Ejector can utilize high pressure energy from liquid mechanism,it can be used in heat pump system coupled with economized vapor injection(EVI)scroll compressor.When running under low temperature conditions,the performance of the EVI system with ejector can be improved further.In this paper,the design method of the heat pump system with ejector is presented,and the process for designing the heat pump with ejector(EVIe)was summarized.One prototype heat pump was designed under the condition of the evaporation ...     

大体积混凝土温升与强度增长的试验研究

针对大体积混凝土结构构件实体强度与普通标准养护试块强度发展规律间的差别等问题,通过研究实际工程尺寸试件温度场的分布和实验室混凝土变温养护试验,以不同养护制度下的试块强度得出了大体积混凝土结构实体强度的发展规律,为工程施工提供了依据,成功地解决了工期与质量的矛盾,取得了较好的技术经济效果.