Aiuminium -3%Copper hot rolling

[philip66]

I needed to reduce the thickness of a strip of al- 3%cu. I heated it to 575 degree c but it fragmented and broke into pieces on rolling. Any one know why? Should i have annealed it?

 

[unclesyd]

Your temperature is way too high, you are almost at the liquidus of the alloy.
I've never seen a Al/Cu alloy heated above 450°F while working as the exposure to the temperature should be limited.
If preheat is necessary try 350°F-375°F and limit the time at preheat to less than 30 minutes.

Come back with the end use and see if additional heat treatment might be needed.

 

[kenvlach]

unclesyd is correct; your temperature is too high.

Fragmentation during hot rolling indicates “hot shortness” due to failure at the grain boundaries. Heating Al alloys above 500^oC results in grain growth (coarsening) and segregation of impurities to the grain boundaries. This can result in a liquid film between the grains even though the overall composition Al-3%Cu is about 20 to 25^oC below the solidus (see phase diagram below, from ASM Int.).

Also, your alloy may have a cored microstructure if it wasn’t homogenized (solutionized) after initial casting. Solidification at reasonable rates forms primary dendrites > 97% Al and a Cu-enriched interdendritic phase (possibly of eutectic composition, m.p. 548^oC). Very slow heating above the solvus temperature, ~472^oC, to allow diffusion, sometimes with intermediate mechanical deformations, is necessary to avoid liquid formation above the eutectic temperature, 548^oC. As solutionizing temperatures can result in excessive oxidation as well as grain growth, it may be best to warm roll as suggested by unclesyd. This processing will also reduce the time needed if subsequent solutionizing is required.

Castings of this composition are also highly vulnerable to hot shortness (hot tearing) during solidification shrinkage, so possibly there were pre-existing flaws. One method to avoid this is addition of at least 3% Si.

Please give a more precise composition and the desired final properties or objective.

 

[philip66]

Thanks unclesyd and kenvlach,
I was reducing the strip of al-cu for a shimming application. I decided to hot roll in an effoet to reduce forces. I did consult the phase diagram and was advised to stay below the liquidus line.I dont have the series number for the alloy.Will i try 350-375 f?

 

[kenvlach]

You apparently have a commercial alloy rather than high purity Al-3%Cu; hence, the solidus and liquidus temperatures will be lower due to additional alloying elements and impurities. A commercial alloy of similar composition is Al 2017 (2.6%Cu, 0.35%Mg). This alloy has a melting range of 955-1185^oF (513-641^oC). Annealing is 2-3 hours at 775^oF (413^oC). Some elongation limits for Al 2017 at elevated temperatures are:
300^oF 15-25%
400^oF 35%
500^oF 45%
600^oF 65-90%
--- ALCOA Aluminum Handbook.
As your material may have embrittled grain boundaries, I would not attempt to achieve these reductions in a single step (try anneal, roll, anneal, roll), nor use the shims in a heavily loaded application.

 

[philip66]

Thanks kenvlach for your sharing your knowledge. I will follow your procedure.