Strong and precise compact produced by giving high plastic energy to powder

在粉末冶金的烧结过程中，坯体中残留的空位会引起压坯的形态变化，降低强度。如果契约没有空缺，上述问题将会减少。本研究旨在通过给予粉末较高的塑性能来制备无空位的完美压坯。设计了新的方法，明确了以下几点。压缩和扭转压实工业纯铝粉用两个模具的装置进行压缩和扭曲。一个模子是固定的，另一个是旋转的，这些模子相互拉力很大。因此，模具之间的粉末会受到高压和严重的扭曲。结果表明：(1)当模具压力为600 Mpa时，充填效率最高可达95%。(2)当模压压力为312 Mpa时，无扭压坯的拉伸强度仅为2 Mpa。强度随模具旋转而增加，在4PI弧度(滑动行程约60 mm)旋转时，强度达到22 Mpa，是模具的10倍。如果粉末与模具之间的摩擦力太大，摩擦辅助反挤压粉末就不能反挤压。此时，如果容器模具向后移动，粉末将借助粉末和容器模具之间的外摩擦力从容器模具和冲头之间的狭窄空间中挤出。该方法表明：(1)为了使粉末成形，无论压制条件如何，最低冲压压力都需要300兆帕左右。(2)抗拉强度达到144 Mpa，与轧制板材相当。(3)显微分析证实了粉末致密性好的原因。

In the sintering of powder metallurgy, the vacancy left in the green compact causes the form change and lowers the strength. If the compact has no vacancy, the above problems will diminish. This study aims to produce perfect compact of no vacancy by giving high plastic energy to powder. New methods were designed, and the followings were clarified.1. Compress and Twist CompactingCommercially pure aluminum powder was compressed and twisted by the apparatus with two dies. The one die is fixed and the other rotates, and these dies pull against strongly each other. So, the powder set between the dies gets high pressure and severe twist. The followings were found: (1) The charge efficiency became high value of 95% at the die pressure of 600 MPa. (2) The tensile strength of the compact with no twist was only 2 MPa when the die pressure was 312 MPa. The strength increased according as the rotation of die, and became 22 MPa, which was 10 times bigger, at the rotation of 4PI radian (Sliding travel about 60 mm).2. Friction-aided Backward Extrusion Powder can not be extruded backward if the friction between the powder and dies is so large. At this time, if the container die is moved backward, the powder will be extruded from the narrow space between the container die and a punch by the aid of outward friction force between.the powder and the container die. This method showed the followings: (1) To give a form to the powder, the lowest punch pressure needed about 300 MPa irrespective of compacting condition. (2) The tensile strength became high value of 144 MPa which was comparable to that of a rolling sheet. (3) The reason why the powder was compacted well was confirmed by the microscopic analysis.