Porosity in Aluminum Castings
Aluminium alloys absorb hydrogen in the liquid state and unless it is removed, porosity will occur in the casting.
Hydrogen in molten aluminium and its alloys derive primarily from the aluminium – water reaction: 2Al + 3H₂O 4 Al₂O₃ + 3H₂ .
Of course, one major source of water vapour is the atmosphere, but other contributors include products of combustion (when melting is undertaken in gas or oil fired furnaces), the use of hygroscopic degassing or fluxing materials, the presence of reactive materials in the melt and hydrated corrosion products on feed material.
The hydrogen formed is absorbed by the liquid aluminium and unless most of it is removed by degassing techniques, porosity will be observed in the casting.
So, an accurate measurement of hydrogen in the melt before casting is essential to ensure that degassing operations achieve the specified quality acceptance value.
The Hyscan II monitors hydrogen during aluminium alloy processing operations by a quantitative reduced pressure technique, and provides the operator with a quantitative measurement of hydrogen in the melt within five minutes of sampling.
The Hyscan II is robust – its rugged design is ideal for the shop floor, simple to operate, mobile and most importantly, has a proven accuracy with less than 5% difference between that of the vacuum sub-fusion method.
Aside from its use as a quality control tool, the Hyscan II is also used for process investigation and for the evaluation of melt treatments. This means lower scrap rates, and reduced energy and labour costs. These financial savings often allow the retrieval of the capital cost of the instrument in less than one year.
This proven method for measuring porosity in aluminium castings has made the Hyscan II a global leader, and it is used by production foundries not only in the UK, but also throughout Europe, the Middle East, the Far East, North and South America.