Al-Li P/M materials with dispersion of ceramic or intermetallic compound particles

采用机械合金化工艺研究了陶瓷颗粒在Al-Li合金中的弥散行为。机械合金化使Al-Li合金能够获得常规熔炼和铸造技术难以或不可能获得的合金。所用基体合金为Al-2.5Li和Al-2.5Li-1.2Cu-0.7 mg，添加2%或6%的Al_2O_3、TiC和A6_4C_3陶瓷颗粒。以机械合金化粉末为原料，采用冷压和热挤压工艺制备粉末冶金材料。为了最大限度地减少活性锂的氧化损失，所有的加工都是在氩气气氛中进行的。对获得的粉末冶金材料进行了金相分析、拉伸试验和时效硬化试验，通过机械合金化获得了细小均匀的陶瓷颗粒在Al-Li合金中的弥散分布。由于弥散强化，获得的粉末冶金材料具有较高的硬度。然而，时效硬化被显著抑制，这可能是由于位错、亚晶界和相界等非均匀析出部位的增加所致。这并不是含Li的粉末冶金材料所特有的，因为在由机械合金化粉末制备的Al-Cu和Al-CuMg粉末冶金材料中也观察到了相同的行为。然而，由于陶瓷颗粒的细小分散，这些粉末冶金材料表现出高强度。添加2VO1%TiC或Al_2O_3的Al-Li-Cu-Mg粉末冶金合金在挤压状态下的抗拉强度可达600 Mpa。进一步增加陶瓷加入量会导致延伸率下降，从而导致抗拉强度下降。这些脆性粉末冶金材料的行为更像陶瓷而不是金属，因为它们的抗拉强度低于根据其硬度换算的值。比弹性模数高达30 GPA，比强度高达225 Mpa，远高于7075-T6。

Dispersion of ceramic particles has been studied in Al-Li alloys by applying mechanical alloying process which enables to produce alloys that are difficult or impossible to obtain by conventional melting and casting techniques. The matrix alloys used were Al-2.5Li and Al-2.5Li-1.2Cu-0.7Mg, and ceramic particles of AL_2O3, TiC and A6_4C_3 were added by the amount of 2 or 6 vo1%. P/M materials were produced from mechanically alloyed powders by cold pressing and hot extrusion. processing was all done in an argon atmoshpere so as to minimize oxidation loss of active Lithium. Metallography, tensile testing and age-hardening behavior were examined on obtained P/M materials.Fine and uniform dispersion of ceramic particles in the matrix of Al-Li alloys was attained by mechanical alloying. Obtained P/M materials showed high hardness due to despersion strengthening. However, age hardening was remarkably suppressed probably due to increased heterogeneous precipitation sites such as dislocation, subboundary and interphase boundary. This is not peculiar to P/M materials containing Li, since the same behavior was observed in Al-Cu and Al-CuMg P/M materials processed from mechanically alloyed powder. Nonetheless, these P/M materials showed high strength due to fine dispersion of ceramic particles. Al-Li-Cu-Mg P/M alloy with dispersion of 2 vo1% TiC or AL_2O_3 showed tensile strength as high as 600 MPa in as extruded condition. Further increase of ceramic addition caused decrease of elongation and thus tensile strength. These brittle P/M materials behave more like ceramics rather than metals, since they showed lower tensile strength than the converted values from their hardness. Specific elastic modulus was as high as 30 GPa and specific strength as high as 225 MPa, much higher than those of 7075-T6.