Melting, unmelted AlSi Microstructure Amdry 2010 powder

[William]

Hi all,
We are studying Metco Amdry 2010 powder.
We have question about the Melting, unmelted AlSi material after spraying.
How did the melting, unmelted AlSi material happen?

Thanks,
Best regards,
William

[LEN WOOD]

Hi William,

I'm sure Gordon will add more, but in the meantime....

In a perfect setup the optimal amount of powder will enter the Plasma stream and be sufficiently melted, propelled and deposited onto the workpiece. In a not so perfect arrangement (with worn hardware, lack of calibration, incorrect parameters, hopper/powder line/injector issues, etc, etc) less material will be satisfactorily processed. With Al Si Polyester turbulence can be an issue where previously 'spent powder' re-enters the spray stream and becomes an undesirable component of the coating matrix.

I hope this helps.

[Gordon]

Hi William

In addition to comments by Len. Unmelted particles are a fact of life. Most good coatings will have some degree of unmelted particles. The reason why, is that the spray process and powders used are not perfect. Powder particles are not perfect in uniformity of size and shape. Larger particles require more heating than smaller particles. Powder feeding and injection is not perfect. The whole process really is a bit chaotic, so we set parameters to cater for the majority and accept a minority of less than perfect. A good coating often displays evidence of a few under-heated particles along with a few over-heated. A poor coating very often will often have a lop-sided relationship between over and under-heated particles.

My use of the word 'perfect' is to mean a system of 100% efficiency or +/- 0 and not an indication that your equipment or powder is less than it should be

[William]

Hi Len Wood and Gordon
Thank for your reply.
Your explanation helped me so much.
After polishing the specimen, we used the etched mode to inspect the microstructure. We saw the tan and bluish phase.
Anybody know? What are the tan and bluish phase?
How happen with that?
Thanks,
Best regards,
William,

[Gordon]

Hi William

If you referring to phases within the Al-Si alloy matrix, then these will probably be a very rich aluminium phase and a very rich silicon phase. You may better understand by looking at the Al-Si equilibrium diagram. (one here). Which is which will depend on the etchant used.