Spraying on Magnesium substrate

[Madila Awalini]

Hi all ...

Anyone has any experience with spraying of a magnesium substrate? I really would like to hear it then .. Please share with me from the basic .. need it for my study ..
Really appreciate it ..

~Madila~

[derek]

I used to spray Al on Magnesium substrate before and have some problem. After blast the Mg, if you leave the substrate in humid air for more then 2 hours, you will see the gray color powder on substrate, the coating will peel off very easy. So please spray Mg immediately after blasting and pre-heat the part is recommended. What is the gray color stuff? I don't have time to analysis it. The blast mediam should be SiC.

[LEN WOOD]

Hi Lini,

I have sprayed many, many Mg components with ZERO problems or failures.

I have sent you an email so that you may contact me directly - I am only up the road from you.

Preheat and SiC?????

[Gordon]

Hi Madila

Generally, you should treat magnesium alloys as you would aluminium, but only more so. You should not directly preheat the surface to be sprayed. Best not preheat at all, just try and keep parts above dew point temperature. Try and spray immediately after surface preparation, as the surface will oxidise quickly.

[Madila Awalini]

Hi All..

Thanks for the practical tips.

I read articles on spraying onto Mg substrates, but they didn't give the exact preparation steps.

I am thinking the same way with Gordon, by not doing preheat on the substrate, cause this material oxidizes so fast and can interfere with the adhesion of coating later on.

But until now, I haven't tried anything on the process.
I think I will try some variations on the prep steps , if time permits, just to see the effects on my specimen.


Cheers,

~Madila ~

[derek]

Hi Gordon,
I come here just want to share my experence and learn some thing from the experts. We can disscuss why this way works but other. This a open forum, why I always saw someone keep the secret and put the personal contact information (AD) in here ???? For $$$$$$$ ?

[Gordon]

Hi Derek

I do agree with your sentiments.

I assume your comments were aim at Len's post. Len normally provides a great deal of helpful input to the forums. In this case the post does seem a little selfish to the forum as a whole.

Quote:Preheat and SiC?????

Could be interpreted as dismissive and arrogant without explanation. I'm sure Len's intentions though were not to offend.

While, I would certainly question/argue the case about use of preheat and SiC grit. I would be foolish to completely dismiss other opinions/experiences. I would certainly make sure magnesium substrates were above the dew point temperature as water condensation will not help. I know direct pre-heating of the freshly prepared coating area is not recommended.

Quote:What is the gray color stuff? I don't have time to analysis it.

I suspect magnesium oxide.

Quote:The blast mediam should be SiC.

I'm not sure it "should" be or will be any better/worse than alumina, but sure its a possible alternative medium.

[Madila Awalini]

Hi Gordon,

What you mean by direct preheating is doing it from the reverse side of the sprayed area, right ?
I'm thinking of varying some preheat distances also to see the effects.
Do you think it's worthwhile doing?
Any other parameter variations that you can recommend ?
From my previous study, I think what you mentioned about the gray color layer being a Mg oxide is probably true.

Thanks all,
~Madila~

(06-23-2010 03:10 PM)Gordon Wrote:  Hi Derek

I do agree with your sentiments.

I assume your comments were aim at Len's post. Len normally provides a great deal of helpful input to the forums. In this case the post does seem a little selfish to the forum as a whole.

Quote:Preheat and SiC?????

Could be interpreted as dismissive and arrogant without explanation. I'm sure Len's intentions though were not to offend.

While, I would certainly question/argue the case about use of preheat and SiC grit. I would be foolish to completely dismiss other opinions/experiences. I would certainly make sure magnesium substrates were above the dew point temperature as water condensation will not help. I know direct pre-heating of the freshly prepared coating area is not recommended.

Quote:What is the gray color stuff? I don't have time to analysis it.

I suspect magnesium oxide.

Quote:The blast mediam should be SiC.

I'm not sure it "should" be or will be any better/worse than alumina, but sure its a possible alternative medium.

[Gordon]

Hi Madila

Quote:What you mean by direct preheating is doing it from the reverse side of the sprayed area, right ?

To clarify: direct preheating would be like using the spray gun or separate heating torch directly on the surface to be sprayed. Indirect preheating would be applied to areas not to coated.

Quote:I'm thinking of varying some preheat distances also to see the effects.
Do you think it's worthwhile doing?

Well, there is nothing to beat a bit of experimentation Even if results are negative to what you want to achieve, experience and knowledge gained of what does not work can be just as important as knowing what does.

I would be inclined to avoid any preheating of a freshly grit blasted magnesium substrate. I would consider preheating just prior to grit blasting and spraying coating immediately while a little residual heat remains.

Quote:Any other parameter variations that you can recommend ?

Not really, only pay extra attention to coating and substrate temperatures during spraying - careful selection of speeds and feeds and placement of auxiliary cooling if needed.

[Madila Awalini]

Hi Gordon,

Thanks for the clarification.
That's what I meant in the first place

And thanks also for your input.
I will definitely need more of them in the future.

Cheers,
~Madila~