How to identify "Grain" in aluminum

scroc · Jan 16, 2017

Hey men, I recently purchased some 7075 plate and blocks from my metal dealer and the blocks were marked with arrows showing how the grain ran.
I cut some pieces on the bandsaw and squared them up on the lathe but was unable to notice any differences in finish or machineing quality while working with this material.
My question is how do I identify how the grain runs and does it make any difference in finish or strength?
steve

Longboy · Jan 17, 2017

From what I am reading, "grain" in metallurgy isn't referring to a visible direction like found in a piece of wood. Rather a multi step process of tempering. The grain size determining the strength of the material. However the material can be rolled to a grain alignment for specific properties. I see terms of process like "eta precipitates" and "eta phase" but don't understand the nomenclature in my kwikie look up! If you are building aviation or marine items.....it matters. Modeling.....unlikely!

https://www.britannica.com/science/grain-solid
https://en.wikipedia.org/wiki/7075_aluminium_alloy

bobm985 · Jan 17, 2017

Grain is usually only a factor when bending. Tighter bends can be made across the grain without cracking, and must be considered when the bend radius is less than twice the thickness, depending on the material and its hardness. Books on presswork can provide specifics. Grain direction is the same as the rolling direction, lengthwise.
Regards,
Bob

Chiptosser · Jan 17, 2017

For hobbyist applications, you don't have to worry about the grain direction.

Unless you are making something 5,10,20 feet long and exposed to many flex cycles.

bazmak · Jan 17, 2017

Certain alum alloys should be folded across the grain.If folded with the grain
it weakens the metal and even cracks.If my memory serves me correctly
what we used to call duraluminiun was prone.Also certain alloys work/age harden which also causes problem.No experience but the aircraft industry
has very strict stds