粉末冶金铝合金烧结致密化过程

以纯Al粉为主要原料,添加Cu单质粉末以及Al-Mg、Al-Si中间合金粉,利用粉末冶金压制烧结方法制备出相对密度98%以上的Al-Mg-Si-Cu系铝合金.研究表明,烧结致密化过程主要分为3个阶段:初始阶段(室温~460℃),坯体内首先形成Al-Mg合金液相,液相中的Mg原子分别扩散至Al或Al-Si粉末中,与Al₂O₃反应并破除氧化膜,形成Al-Mg-O等化合物;同时,Al-Cu发生互扩散,形成Al₂Cu等金属间化合物.第二阶段(460~560℃),Al-Cu、Al-Si液相快速填充颗粒缝隙或孔洞,坯体相对密度显著提高;此阶段的致密化机制主要是毛细管力引起的颗粒重排,以及溶解析出导致的晶界平直化.第三阶段(560~600℃),随温度的升高,液相润湿性提高,晶粒快速长大,使得大尺寸孔洞填充,烧结体基本实现全致密,此阶段的致密化主要由填隙机制控制.在铝合金晶界处发现了MgAl₂O₄和MgAlCuO氧化物的存在,推测Al粉表面氧化膜的破除机制与合金成分有关.由于Al-Cu液相在Al表面的润湿速率远高于AlN的生长速率,因为在本体系中未发现AlN的存在.

Sintering densification process of powder metallurgy aluminum alloy

In this study, an Al-Mg-Si-Cu alloy was prepared by conventional press-and-sinter powder metallurgy techniques using pure Al powder, Cu element powder, and binary Al-Mg and Al-Si powders to investigate the processes of atom diffusion and microstructure evolution. The relative density of the sintering samples exceeded 98%. It is found that the sintering densification process can be approximately divided into three stages. In the first stage (from room temperature to 460℃), after the Al-Mg eutectic liquid phase formed at 450℃, the Mg atoms in the liquid diffuses into Al and Al-Si particles and reacts with Al₂O₃ at the metal/oxide interface to form an Al-Mg-O compound. Meanwhile, the interdiffusion between Al and Cu leads to the formation of Al₂Cu compounds. In the second stage (from 460 to 560℃), the micro-channels or small holes between the grain boundaries are rapidly filled by Al-Cu and Al-Si eutectic liquids, which leads to a significant increase of density. In this stage, the densification mechanisms are particle rearrangement controlled by the capillary driving force and contact flattening dominated by solution-reprecipitation. In the last stage (from 560 to 600℃), the residual large holes are finally filled by the liquid because of the enhancement of wettability and grain growth with the increase of sintering temperature. In this stage, the densification mechanism is mainly pore-filling, resulting from the grain growth. The sample is fully dense through this stage. In addition, MgAl₂O₄ and MgAlCuO compounds are found in the grain boundary region; thus, it can be speculated that the mechanism of oxide film disruption is related to the alloy composition. Furthermore, because of the good wettability between Al-Cu liquid and Al, the surface of Al particles is quickly wetted by the liquid under the capillary driving force; therefore, no AlN is found in the grain boundary region in this research.