原位TiB_2颗粒对7075铝合金凝固组织的影响

Solidification Microstructures of 7075 Aluminum Alloy with In-situ TiB_2 Particles

采用原位反应制得了纯净的Ti B2/7075复合材料。研究表明,随着Ti B2颗粒含量增加,树枝状的7075铝合金逐渐转化为细小的蔷薇状,Ti B2颗粒含量增加到4.5%（质量分数）时α-Al晶粒尺寸达到最小,之后又重新转化为粗大的树枝晶。3%Ti B2/7075合金的晶界处Ti B2颗粒尺寸一般在900－1400 nm,Ti B2颗粒大致呈六边形或四方形。当颗粒含量达到9%时,大尺寸的Ti B2颗粒分布在晶界处,晶界附近的晶核内弥散分布着大量细小的Ti B2颗粒,尺寸在100－400 nm左右,形状为不规则的多边形,细小的Ti B2颗粒容易在固/液界面被捕获,产生颗粒推移效应。在720℃保温发现,3%,6%,9%Ti B2/7075复合材料中Ti B2颗粒的平均沉降速率分别为2.308×10-6,1.146×10-6,0.371×10-6m·s-1,原位颗粒增多,抗沉降能力增强。

Novel reactive technique was employed in the synthesis of 7075 Al matrix composites. The results indicated that the grain size of the Ti B2/7075 composites decreased with the increase of the Ti B2 particle content,and α-Al became rosette grains from dendrites. The grain size of 7075 aluminum alloy was the minimum when the Ti B2 content was 4. 5%,afterwards the grain became large dendrites again. Hexagon or square Ti B2 particles were about 900 － 1400 nm in size in 3% Ti B2/7075 composites. When the content was up to 9%,Ti B2 particles with large size were distributed in grain boundary area,and a large number of scattered small Ti B2 particles with size of 100 － 400 nm were irregular polygon near the boundary inside the nucleus. Tiny Ti B2 particles were engulfed easily in the interface,bringing about the pushing of Ti B2 particles. Ti B2 particles grew into nearly six-side prisms during the process of free solidification at the pouring temperature of 720 ℃. Then the Ti B2/7075 composites were subjected to heat preservation at 720 ℃,and the results showed that the anti-settlement behavior increased with the increase of in-situ particles. The sedimentation rates were2. 308 × 10- 6,1. 146 × 10- 6and 0. 371 × 10- 6m·s- 1in 3% Ti B2/7075 composites,6% Ti B2/7075 composites and 9% Ti B2/7075 composites,respectively.