Short version:

Is it a physical problem (crystal structure/grains/redox/etc.) or just a logistics problem (keeping the solutes from homogenizing, molten/solid/temperature related problems) that keeps us from commonly employing objects that have transitioning alloy compositions throughout the object?

Long Version:

I was reading more into the designations of various metals and starting thinking about something.

Is there a reason why we don't see materials where the alloy composition is (significantly) different in one part of the material than the other. For example, if a molten starts freezing and we introduce in more of other materials. Lets say we wanted to make a aluminum wing for a plane that was corrosion resistant but a bit stronger than our homogenous metal of choice (6061 for example). While making a 6061-aluminum wing if the exterior were to cool until it was no longer molten, could I not then inject some other solute into the molten still aluminum (for example copper/manganese/magnesium for 2024 aluminum).

My intuition tells em this happens to a small extent with various steels when we treat their surfaces in a coal-heated environment, since we introduce new carbon into the iron. The only problems that seem apparent to me is if there are significant changes in crystal structure between the two(or more) alloys, but even so wouldn't one expect a gradient between various alloy domains? Why isn't this something we see around more often?

  • $\begingroup$ In addition to case-hardening mild steel tools on the forge, differential tempering and the welding together of parts made of different steels followed by differential tempering have been used and that is just listing the things that craft metal-worker have gotten up to over the years. With the rise of scientific metallurgy I imagine that a lot of things have been tried, but it is always going to come down to specifications and money. Do you actually need that and do you need it badly enough to pay what it costs? $\endgroup$ – dmckee --- ex-moderator kitten Aug 2 '14 at 23:12
  • $\begingroup$ The term you are looking for is Functionally Graded Material, which is perhaps broader than your initial question. As you intuited, making any complex shape with an FGM is difficult at best. $\endgroup$ – Jon Custer Aug 3 '14 at 0:12

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