23 Mar 2020

Powder Compaction Process

Composites have become widely used in aerospace and automotive applications, including for many critical components such as pistons and conrods, and other structural elements.
 
In particular, the ability to deliver high strength at light weight has made composite materials highly valued. Other properties enhanced in composites components include the part stiffness, hardness, and wear resistance.  Aluminium is often combined with other alloying or reinforcing elements to enhance its strength. Aluminium has many applications in structural engineering, electrical and electronic engineering, and consumer products. While aluminium is not as strong as other metals, such as steel, it is one of the lightest metals which provides a high strength-to-weight ratio.
 
These properties have made it a focus for research, as well as a useful material in industrial applications. Graphene oxide (GO) which is hydrophilic (unoxidized graphene is hydrophobic), has remarkable mechanical strength, and capabilities for molecular-level chemical sensing.
 
06a-CROP-2017-07-20-Specac-Products-2309
In this application note, the manufacture of Al-graphene/GO composites by compaction and sintering of powders has been investigated.
 
Method & results
The main steps in the process are as follows. First, the component powders are mixed and well dispersed by various means including the use of solvents, then dried, or directly by dry ball milling.
 
Then the powders are transferred to a 20mm Atlas® evacuable pellet die and compacted at pressures ranging from 30MPa to 560MPa using a Specac Atlas® Autotouch 40T hydraulic press, resulting in a green compact. Finally, the compacted powders are sintered at 600°C in an inert atmosphere to produce the final composite material. To establish a base point of comparison for the composites, pure aluminium powders were also compacted and sintered.
 
The properties of both the green compact and the final composite are dependent upon the compaction parameters.
 
Uncontrolled compaction leads to high levels of variation for compaction efficiency in the samples produced, as well as wide variation in the load failure levels of these samples.

With the Specac Atlas® Autotouch 40T Press it is possible to ensure control of the pressure level, ramp rate, and dwell time. The controllability and reliability of these parameters is a major benefit in producing samples with more uniform properties.
 
The control of these parameters also allows the compacting process parameters to be optimized by a design of experiments method. The maximum pressure levels achievable, up to 780MPa for the 20mm die, allow a wide range of compaction pressure level setting, and are high enough to allow for direct comparison with larger scale industrial production equipment.
 
Conclusions
The Specac Atlas® Autotouch press offers precise and flexible control of the powder compaction process, resulting in aluminium matrix composites with consistent properties.

Controllable parameters include the applied load, load hold time, and the rate of load release. The applied load may be maintained indefinitely with the press’s Auto Top-Up feature, or held for a pre-determined period ranging from 0.1 to 99.9 minutes. The programmable features of the press are ideal for conducting systematic optimization of compaction processes via the design of experiments approach. Up to 6 optimised press programmes may be stored in memory.