铝合金搅拌摩擦加工原位反应生成物颗粒增强机制

在1100-H14铝合金基体表面开凹槽添加Ni粉进行搅拌摩擦加工(Friction Stir Processing,FSP),利用Ni粉在搅拌过程中的碎化及其与基体的原位反应生成的高强、高硬的金属间化合物制备强化的表面复合层。结果表明,不同于添加陶瓷颗粒的FSP工艺,Ni颗粒能在搅拌过程中充分碎化,并与铝基体原位合成金属间化合物,原位自生的增强体颗粒与基体是以金属键合的方式结合在一起,因此与基体金属间具有良好的界面相容性和界面结构,能够很大程度上改善颗粒的强化效果。增强颗粒与基体结合界面的性质对复合层硬度的影响非常显著,为了提高复合层硬度,提出了通过原位反应获得颗粒/基体的高强界面的模型。

Strengthing Mechanism of in-situ Synthesized Particles in Friction Stir Processed Aluminum Alloy

Friction stir processing (FSP) was conducted by using aluminum alloy plate 1100-H14. Prior to stiring, a rectangular groove was machined on the plate along the center of stir pass, in which nickel powder was filled. Via in-situ synthesis during the processing thermal cycle, Ni particles in Al base metal would react with Al to form hard particles of NiAl intermetallics. Thus, a composite layer would be fabricated. The results show that Ni particles were stir-crushed to pieces and NiAl_3 reactive particles, in submicron size, were formed. A portion of NiAl_3 particles were further refined by stir-crushing. The microhardness test shows evident increase of the hardness distributions in the composite layer. Compared with ceramic powders added in FSP, physical models were proposed to describe both particle-strengthing mechanisms. In-situ synthesesed intermetallic particles have the crystal boundaries to base metal with strong metallic bonds (twinned crystal boundary, for example), which makes difficulty for dislocatons to pass around that forms crystal boundary strengthing mechanism, whereas the stir-crush refined particles issue fine particle dispersive strengthing mechanism. However, in the friction stir processing by adding hard ceramics particles, much weak bonds between particles and base metal contributes little material strengthing as dislocations may easily pass around.