脉冲电变质处理纯Al凝固晶粒组织形成计算机可视化模拟

研究了电变质处理形成的纯Al凝固晶粒组织。试验过程中对不同电脉冲冲击能量下的过冷度数值进行实测,在此基础上利用连续形核模型和枝晶尖端生长的动力学模型即KGT模型模拟了纯Al凝固晶粒组织的形成过程。计算了该组织的凝固晶粒组织特征值,包括晶粒密度和平均晶粒尺寸,并与实测数据进行了对比。试验结果显示电脉冲冲击能量从0 J增加到270J时,过冷度随脉冲能量的增加而从6℃增大到14.1℃,最大形核密度从1.99×104个/m2增大到1.991 87×108个/m2,最大晶粒形核密度提高四个数量级。经过对比模拟结果与试验结果符合较好。

电脉冲变质处理对ZL108合金性能的影响

在液态条件下对ZL10 8合金进行电脉冲变质处理 ,结果表明 :经电脉冲变质处理 (EPM)后 ,ZL10 8合金的凝固组织呈现磷变质的特征 ,经热处理后 ,力学性能明显提高 ,说明该技术可以作为一种变质处理的替代方法应用于为提高合金耐磨性的ZL10 8合金中 ,并表现出良好的抗衰退性。

电变质设备的研制及铸件成形的质量分析

研制一种用于金属铸件电变质处理的大电流可控电脉冲发生装置,其脉冲电流的最大峰点值可达1.7MA,采用单片机实现电容器组的充放电时间的控制,设置充放电时间范围为1～9999ms。装置的电流频率达到超声波频率范围,最大为1.1MHz。Al 4%Cu合金石膏型铸件的电变质处理实验结果表明,铸件中宏观疏松和热裂纹消失,晶粒细化,铸件表观质量得到改善。

Surface Reactivity in Tropical Highly Weathered Soils and Implications for Rational Soil Management

Highly weathered soils are distributed in the humid and wet-dry tropics, as well as in the humid subtropics. As a result of strong weathering, these soils are characterized by low activity clays, which develop variable surface charge and related specific properties. Surface reactions regarding base exchange and soil acidification, heavy metal sorption and mobility, and phosphorus sorption and availability of the tropical highly weathered soils are reviewed in this paper.Factors controlling surface reactivity towards cations and anions, including ion exchange and specific adsorption processes, are discussed with consideration on practical implications for rational management of these soils. Organic matter content and pH value are major basic factors that should be controlled through appropriate agricultural practices, in order to optimise favorable effects of colloid surface properties on soil fertility and environmental quality.