稀土镁合金的超声制浆及其高压流变成形下的非平衡组织控制

As a new kind of structural materials, magnesium alloy has to be further strengthened and corrosion-resistance reinforced in order to expand its usage and utilized amount. One of the important measurements for the strengthening and toughening of magnesium alloys is Rare Earth(RE) alloying. However, there are also a series of problems existed in RE-alloyed Mg alloys, such as un-uniform distribution of RE-containing phases and not high-enough toughness, and these bring out difficulties in casting and rolling processes. Therefore some new processing techniques have to be developed. In this proposal a new processing technique named UVHP process- - Ultrasonic Vibration and High Pressure Rheoforming process- - has been proposed out for RE-containing Mg alloys, i.e., high-pressure rheoforming after ultrasonic slurry-making. With high-energy ultrasound to make semi-solid slurry, and by utilization of the high-cooling rate under high-pressure forming, the crystals of RE-containing Mg alloys can be significantly refined, and non-equilibrium structure can be obtained, such as quasicrystals, etc. With these measurements, the strength, elongation and heat-resistance of Mg alloy parts can be significantly increased. Through deeply research on the cooling behavior and forming mechanism of non-equilibrium structures of RE-containing Mg alloys under high-energy ultrasound field and different pressure field, the controlling principals of non-equilibrium microstructure during squeeze-casting of Mg alloy parts, such as quasicrystals, can be obtained. These will provide theretical foundation for the development of new forming processes for Mg alloy parts.

镁合金作为一种新型结构材料，要扩大用量及用途，必须进一步提高材料的强度及抗腐蚀等性能。镁合金强韧化的重要途径之一是稀土（RE）合金化，但稀土镁合金存在稀土相分布不均等一些严重的问题而造成铸造和塑性加工困难，必须开发新型的成形加工技术。本申请提出针对稀土镁合金的超声制浆及其高压流变成形技术方法（UVHP-Ultrasonic Vibration and High Pressure-rheoforming），通过高能超声制备半固态浆料，以及浆料的高压流变成形下的较快冷却速度，使稀土镁合金的晶粒大幅度细化，并获得具有准晶等非平衡凝固组织，达到大幅度提高稀土镁合金零件的强度及韧性的目的，并增强耐热性等综合性能。通过深入研究高能超声场、不同压力场下稀土镁合金的过冷行为及非平衡凝固组织的形成机理，获得镁合金零件挤压成形中准晶等非平衡组织的控制原理，为开发镁合金零件的新的成形工艺技术奠定理论基础。

作为一种新型轻质结构材料，镁合金要扩大用量及用途，必须进一步提高其强度及抗腐蚀等性能。镁合金强韧化的重要途径之一是稀土（RE）合金化，但稀土镁合金存在稀土相分布不均等一些严重的问题而造成铸造和塑性加工困难，必须开发新型的成形加工技术。本项目研究开发出针对稀土镁合金的超声制浆及其高压流变成形技术（UVHP—Ultrasonic Vibration and High Pressure-rheoforming），通过高能超声制备半固态浆料，以及浆料的高压流变成形下的较快冷却速度，使稀土镁合金的晶粒大幅度细化，并获得具有准晶等非平衡凝固组织，达到了大幅度提高稀土镁合金零件的强度及韧性的目的，并增强了耐热性等综合性能。在0--400MPa流变挤压成形压力下，稀土镁合金的抗拉强度随压力增大而增大，且伸长率也是同时增大。在更高的高压（400MPa--800MPa）作用下，力学性能增加的效果逐渐减小，研究结果为优化稀土镁合金的流变挤压成形压力奠定了理论基础。开发出一种新型Mg-6Zn-3RE-1.4Y（RE-混合稀土）稀土镁合金材料，并获得了稀土（RE）含量对Mg-Zn-Y-RE稀土镁合金高温性能的影响规律。在0--3%RE含量范围内，室温性能在1%RE左右性能最高，但高温力学性能随RE含量的增加是一直增高的。本项目为开发新型稀土镁合金及其零件的高压成形工艺技术奠定了技术基础。