Your question is difficult to answer because there are many variables involved. I'll try to answer some of that by relying on past experience and the various PQR tests I've been involved with. Metallurgical questions will require someone else's input.

Generally, I like to think in terms of weld volume for comparisons. For a given joint volume, larger wire USUALLY results in fewer weld passes to fill the joint. However, with FCAW or MAG, it is possible to increase the amperage/wire feed speed so that 0.045" dia filler metal has a weld deposition rate nearly equal to the 0.062" dia electrode welded at it's middle range. Which means both wires could require the same number of passes to fill the joint. So that depends on your welding parameters. And, of course, that doesn't mean you can weld at high ranges in all situations, just that on a bench you can make the filler metal do things it wasn't supposed to do.

Welding at the higher ranges USUALLY generates more spatter. It represents lost metal and lost energy. However, that can be minimized by technique, direction of travel, electrical stick out, etc., or even different shielding gases. So again, that is not a firm rule.

And you also have to consider travel speed, which can affect the overall heat input, number of weld passes, deposition rate, and so forth. Tests I have run show that you can expect differences on metallurgical properties when varying welding parameters while using the same spool of wire.

Actually, in typing this I am reminded of the wisdom in qualifying weld procedures whenever the essential variables are exceeded. There are simply too many ways to change the nature of weld metal. So it is best to choose how you want to do the welding and then test to prove the suitability.

Sorry I can't be of more help. I suggest that you collect product data literature from various manufacturers and compare their information on deposition rates and parameters. I have found them to be pretty accurate when compared to my own PQR tests.

Hope all works out for you,
Chet Guilford

Hello again Sreenathbabu!
Just as I mentioned in my previous reply, you need to include more specific information. However, this post does contain more, and yet not enough. No offense! Let's try to break it down:

(1) Deposition Rate: This will vary, and is very dependent on having optimal welding parameters for each diameter filler "wire". If optimal welding parameters are set for each diameter, then the result usually is an increased deposition rate. Now, if let's say none of the parameters are adjusted when the filler wire is "switched"(changed) from 0.8mm to 1.2mm then, the deposition rate will not increase as much. Furthermore, if the welding parameters are'nt adjusted when switching from one wire diameter to the other, then the appearance and quality of the welds will be different. What I mean is: if optimal welding parameters are set when welding 0.8mm diameter, then you change the diameter but, you do'nt change the welding parameters, the end result will be that there maybe a slight increase in deposition rate, because of the larger size wire but, most importantly, the quality of the weld deposited will suffer!!!
Increased amount of spatter, less penetration, less fusion at the "toes of the weld, excess reinforcement on the "crown"(face) of the weld etc.
Finally, I have to agree with Chet's example when he mentioned about increasing amps/wire feed speed so that .045'' dia. can have a weld deposition rate nearly equal to .062 dia. electrode welded at it's middle range, and everything else he mentioned after this.

(2) Heat input to the base metal: This factor will not change mathematically if you Do Not adjust the welding parameters when changing from 0.8mm dia. to 1.2mm dia. filler wire when you calculate the amount of joules/newtons. However, if you consider the many other factors involved in order to accurately compare the difference in heat input to the base metal well, let's just say that it gets more complicated with regards to all of the factors you have to consider, and I'll just name a few: (A) The diameter increase or decrease will have an effect in the ACTUAL heat input to the base metal (basic electrical theory and physical laws). (B) Cladding or padding as opposed to welding a joint together. (C) "Pushing or pulling" the direction of travel angle. (D) Joint design. (E) Carbon Equivalent or "CE" of the base metal. (F) Alloying elements. (G) Metal Inert Gas as opposed to Metal (re)Active Gas. (H) Choice of metal transfer (Short circuit, Globular, Spray, and adding pulsing of volts/amps.
(I) Travel speed, wire stickout, shielding gas flow rate, gas mixture, etc.
In other words alot of factors!!! Finally if you do adjust to optimal welding parameters for each diameter, then you will change the heat input to the base metal

(3) Microstructure: TOO Many factors have to be considered here so, because I'm not a metallurgist I may end up "sticking my footus in my mouthus". In other words, like Chet, I think I'll pass as far as getting into any details about this factor. The only point I'll make is how the amount of heat input affects the microstructure of not only the weld but also the base metal in the heat affected zone(HAZ).
In other words, too much heat input will have a detrimental affect to the microstructure of the weld, and base metal. Not enough heat input will also have a detrimental affect to "fusion zones" of the weld(lack of fusion), and lack of coalesence. Ultimately, only by testing, will you see the difference in microstructure as it relates to heat input, filler metal composition selection, gas selection, purity, and amount of diffusable hydrogen in the filler metal. Speaking of this, if you are welding on metal above a certain thickness, then preheating has to be considered in order to relieve not only moisture but, also internal stresses in the joint when tacked together prior to welding. the same is true after welding where post weld heat treatment(PWHT) may be needed to stress relieve. I might have mentioned too much already!

(4) Hardness: This will generally be affected by the amount and type of alloying elements in the filler metal, and the amount of diffusable hydrogen, "CE"(carbon equivalent), etc. Heat input also affect hardness if you really think of it. Again, so does PWHT. Also, Gas selection can in certain instances alter the amount of heat input, therefore affecting the microstructure which in turn, affects the hardness. Finally, I'm sure there are more variables but, I think I'm writing a reply that may be taking too much "webspace" so, I'll leave it at that.
Before I go on to (5), do you notice how all of these factors interelate to the welding parameters? Finally, I'll try to explain (5) and (6) together so I do'nt tale too much space.

(5 and 6) I think that these 2 factors were best explained in Chet's reply to you so I'll leave his response alone by totally agreeing with him.
I'll ony mention that, as a general rule, if the voltage is'nt set high enough,and the wfs(wire feed speed) is set to the correct amount, the you'll have excess spatter(spalls). The same is true when you reverse the "scenario". In other words, Too much wfs and not enough or correct voltage will result in excess spatter. other factors can cause excess spatter such as: increased magnetic field in the weld area which causes the infamous "arc blow", will cause excess spatter and affect other factors previously mentioned. Gas selection and gas mixture will definitely determine spatter "behavior" and the amount (the little buggers!!!).

In summary, and I know I could've mentioned this before but, the internet is a fascinating space to explore (cyberspace). So I encourage you to explore some the manufacturer websites to review some of their data. One of the best websites for MIG-MAG welding (GMAW, FCAW) is located at: www.weldreality.com . The producer of this site is Ed Craig.
I know that you will enjoy this site because of the amount of knowledge and experience Ed puts in this repository. One more thing that I'd like to mention is that you can also field this. and any other question in his website, and he'll be very prompt about responding to you.
With that, I hope that you can find the information that you seek in order to complete your experiments, and good luck!

Respectfully,

SSBN727 Run Silent. Run Deep!!!

The variation of wire diameter has great effect on any weldment.
Not metalurgical effects, but operational effects. Metallurgically, a weld is a weld. Varying wire diameters can influence heat inputs, though. This, in itself can influence microstructure, hardness, etc.
Preheat / postheat can effect this as well.

Certain wire diameters can only supply certain arc characteristics in certain circumstances.

Don't have enough info on what you are doing to answer any more but in very general terms.

Increasing / decreasing wire diameters may or may not work on your particular joint configuaration.
Example-.035 wire may be in axial spray arc at 180 amp, but you can be sure that 1/16 wire won't.

The key thing to keep in mind is the thought of arc density. Arc density is the relationship of weld power (amps x volts=watts) and the wire metallic cross-section.

Because of arc density, smaller wires tend to give more penetration and always a higher deposition rate, within reason, at a given set of parameters. You'll find this particularly true in T1 flux core, although it applies to all wire welding processes.

Don't know if I helped or hindered here.

A few more particulars would be very welcome!!

Keep in touch!

Good Luck

brande