【作者】 张秋元；

【导师】 田永生；

【作者基本信息】 山东大学 ， 材料学， 2010， 硕士

【摘要】 摘要本文利用激光强化技术,采用高功率连续波的YAG固体激光器对预置了Ni、Ti等粉末的2024铝合金基体表面进行激光强化处理,以期原位反应生成铝的金属间化合物,从而提高铝合金表面的硬度、耐磨损及耐高温抗氧化性能。在氩气保护的条件下,采用适宜的激光强化工艺参数和粉末组合,可在基体表面制得厚度为1～2mm,组织致密,且与基体呈现良好冶金接合的合金强化层。对强化层的微观组织结构分析结果表明,强化层主要由NiAl、Ni3Al、NiAl3、Al3Ti、AlTi等金属间化合物与分布在它们之间的α-Al固溶体组成,并形成了多层次的组织结构。表层主要由细小胞状晶枝组织构成,并出现了大量纳米级组织颗粒；内层组织呈多样性分布,组织生长具有很强的方向性；接合部则是由垂直于界面生长的柱状晶组织构成,从而提高了强化层与基体的接合性能。强化层性能受激光参数影响很大,激光功率密度影响熔池的对流强度,扫描速度影响熔池的冷却速度。在一定的激光功率密度下,扫描速度越大,得到的组织颗粒越细小,强化层硬度越高,同时其厚度会变薄,但扫描速度过大时会导致层内出现裂纹。在预涂粉末厚度0.3mm,激光功率密度为700～800W／mm2,扫描速度12～14mm／s,搭接率30%,保护氩气的流量为20L/min处理条件下能得到质量较好的强化层。几种合金粉末的激光强化层硬度均比基体有了显著提高,强化层平均硬度值可达350HV,较基材2024铝合金硬度提高了近2倍,而耐磨性能提高4倍以上,且具有较强的高温抗氧化性能,强化层在连续24小时,400℃的环境中层内未出现开裂现象。更多还原

【Abstract】 A strengthening layer was fabricated on 2024 aluminum alloy by laser surface modification with pure Ti, Ni and Ti+Ni mixed powders in order to obtain in-situ formed aluminum intermetallics for improving the properties of the Al 2024, such as surface hardness, wear resistance, high temperature and oxidation resistance, etc.With proper processing parameters the qualified strengthening layer of about 1～2 mm thick was formed. The analytical results of microstructure and wear properties of the strengthening layer showed that the strengthening layer was composed of the intermetallics such as NiAl, Ni3Al, NiAl3, Al3Ti, AlTi etc. in the form of fine dendrites distributed in a-Al solid solution. The strengthening layer can be divided into several micro-layers:the surface layer is primarily formed of the small cellular-like crystal sticks and a large number of nano-particles; the microstructure of the inner layer is varied and has a strong directional; the microstructure near the substrate is columnar and grows perpendicular to the interface, which improves the bind strength between the strengthening layer and the substrate.The properties of strengthening layer are greatly influenced by laser parameters and the convection strength of melt pool is affected by laser power density. Given laser power density, with a higher scanning speed, the coatings with a finer microstructure, a higher hardness and a thinner thickness can be obtained. However, excessive high scanning speed will result in the crack of the coatings. According to the experimental results, a set of proper parameters of laser power density:700-800W/mm2, scanning speed:12-14mm/s, overlap:30% and argon flow rate:20L/min, was obtained:The results showed that the average hardness of the layer was more than 350 HV, which was much higher than that of the A12024 substrate(less than 120 HV). The wear resistance of the strengthening layer was 4 times higher compared with the Al 2024 substrate. The strengthening layer also has a strong oxidation resistance at elevated temperatures compared with the coatings laser fabricated with TiC50%+SiC50%. Exposed to 400℃for 24 hours, the latter was crack but the former wasn’t.更多还原