Metal Alloy and Viscosity 1

[eranglr]

Hi,

I have a question regarding a Metal alloys and their viscosity.
I know that pure metals go from solid into liquid without a 'glass state' when heated. (not like thermoplastic for example, which goes from solid into plastic state when heated).

Does metal alloys behave differently? are there metal alloys that when heated to a specific temperature reach to a 'plastic like' state, for example - like honey or peanut butter ?

Will appreciate your thoughts on this matter.

 

[EdStainless]

Most engineering alloys have a wide melting range (look at phase diagrams).
So over a range of 100-300C there is a slush, a mixture of solid and liquid.
And the composition is changing over the range. These mixtures are sometimes thixotropic.
This is used is some cases (such as with Mg) to allow injection molding in the slush state.

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P.E. Metallurgy, Plymouth Tube

 

[eranglr]

Thank you for your answer.
Are there rheopectic metal alloys?

 

[tbuelna]

Look at solid state welding processes like friction welding or stir welding.

 

[Ron]

Hey Ed....check your temps again.....factor of 10 low?

 

[arunmrao]

Ed, refers to the solidification range, which can be as high as 300C. It is not the melting point , which can be of 5-10 times high.

Erangir, can you please explain your interest in rheopectic phenomenon. As metallurgists we are concerned about increase in viscosity ( loss of fluidity) with decrease in temperature. Physicists might have a different approach.

I finally hope this is not a student question.


"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

 

[tbuelna]

erangler-

As EdStainless noted there are semi-solid casting processes that take advantage of some non-ferrous metals in the condition you describe to produce parts with very fine detail.

https://en.wikipedia.org/wiki/Semi-solid_metal_casting

Friction/stir welding use friction heat and relative motion at the weld interface to create a metallurgical bond with the materials in a plastic state. These are considered solid state joining processes, since the metal does not experience a phase change between solid & liquid like fusion welding processes. Stir welding is mostly limited to light alloys like aluminum. Friction welding can be performed with almost any metal alloy.

 

[EdStainless]

What I was trying to point out is that alloys do not have a melting point, they have a liquidus and a solidus temperatures, in between which there is both liquid and solid. The fractions and compositions very depending on temperature. And the fluid properties will as well.
This is on top of the changes in viscosity with temperature once you are fully liquid.

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P.E. Metallurgy, Plymouth Tube

 

[arunmrao]

@eranglr

Perhaps if you look for information under " Semi Solid Processing", it will help.



"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

 

[eranglr]

Arunmrao,

My interest in the rheopectic phenomenon is the ability to be to 3D print metal in it molten state.
A few people tried to do this and discussed this.

Thermoplastic have a very good viscosity controlled zone. I'm afraid that when I'll try to print a metal alloy, since it's half liquid-half solid, the output won't be smooth as with polymer 3d printing.

Look also at this.

And no, it's not a student question

 

[arunmrao]

I am familiar with the work being done by this group, thus in my previous thread , I had referred to semisolid processing.

Maybe, you have to adopt a 2 stage process, first cast them using 3D printing technology and then to further improve the integrity of the casting, use squeeze casting technique. I am no expert , perhaps you may contact Prof Thiel in Northern Iowa Univ, who have recently added 3d moulding facility.


"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

 

[tbuelna]

One obvious issue with depositing a semi-solid flow of metal onto a substrate of similar but cooler material is producing a bond between the layers. How would this process provide any benefit versus existing metal laser sintering techniques?

Here's my suggestion for a 3D metal component manufacturing that I've never seen anyone do. Remember the early type of 3D prototype machines that made parts from stacked layers of laser cut paper plies? If you need a 3D component made of very high quality metal, why not use the same process with thin plies of cold rolled, vacuum melt materials. After trimming and stacking the metal plies, they could be consolidated by HIP-ing.

 

[eranglr]

tbuelna -

https://www.youtube.com/watch?v=5s0J-7W4i6s

 

[tbuelna]

eranglr- Thanks for the link! I have not seen that before. Pretty close to what I had in mind though.

 

[metman]

What I was trying to point out is that alloys do not have a melting point

This is true except for eutectic alloys that melt at a specific temperature so there is no slush or plastic temperature zone for these alloys.

Design for RELIABILITY, manufacturability, and maintainability

 

[Maui]

If you plan to 3D print an alloy which has a eutectic region in the phase diagram, then the composition should be adjusted so that you are very close to the eutectic point. The temperature would need to be controlled very precisely if 3D printing of the alloy is to be successful. But it is possible. A good example of this is a tin-lead solder with a composition of 63 weight percent tin and 37 weight percent lead. For this alloy the eutectic point occurs at a temperature of 183 Celsius.

Maui