Aurolia Success Stories
Aurolia enables surface finishing.
Report indicates: Production process can
hinder the finishing of alloy AW 7075.
“This material is not coatable. This alloy is not suitable for decorative processing.” – This is the information that some manufacturers pass on to their customers. Thus, many alloys are initially labeled by producers as unsuitable for anodizing or hard anodizing. Aurolia wanted to demonstrate that in many cases it is indeed possible, focusing on a particularly common material: Alloy AW 7075 in the T6511 temper.
So far, the prevailing opinion is that surface coating of AW 7075 is not possible. The component we coated illustrates the issue: Everything is fine on the top and bottom of the part, but there is a dark edge visible on the outside. The question is: how does it occur and how can it be prevented?
The stretching process prevents
uniform coating application.
Our suspicion: In this material condition, the reason lies in the manufacturing process itself. In condition T6511, the alloy undergoes stretching. This creates hardenings in the edge area, which are visible as a dark border after coating. The stretching process can also be recognized externally with a trained eye. Discolorations with streak patterns in the longitudinal direction of the workpiece indicate the tensile forces acting on the material during production.
These surface irregularities caused by the stretching process prevent the uniform application of the coating layer. To prove this, we enlisted an expert in metallurgical investigations and failure analyses. Three material disks with diameters of 200, 250, and 300 millimeters were tested. And indeed: During the material hardness test, a difference of over 50 Brinell was observed between the edge and the core—where the losses increase proportionally as the component diameter increases.
Machining the edge
enables coating.
To demonstrate that the heterogeneous surface structure caused by stretching is responsible for the poor coating results, we conducted another experiment in which we removed the hardened edge area of the workpiece. Since EN AW 7075 is very machinable, this is also not a problem for most manufacturers. And this test confirmed our suspicion: When the hardening in the edge zone is removed, the alloy can be coated very well and evenly.
Appraiser Dipl.-Ing. Martin Hoffmann attests, ‘Successful coating of this material under typical coating conditions is only possible with sufficient machining allowance to completely remove the deposited structure zone, as indicated by the results of the conducted examinations.’ So, the solution is quite simple: If manufacturers provide the workpiece with some machining allowance and machine off the hardened edge, the previously considered unsuitable for coating alloy AW7075 in the T6511 temper can be excellently and evenly coated.
So, the next time you hear from a manufacturer that the desired material unfortunately cannot be coated, feel free to contact the surface professionals at Aurolia. Together with our experts, a very good solution can often be found even for the difficult cases.
Contact us now and together let’s find your perfect custom coating solution!