Yes, this information is available in a text. In most any basic text of metallurgy.
Physical Metallurgy Principles 3RD Edition Robert Reed Hill Practical Metallurgy & Materials 5TH Edition John Neely Serveral more you can find at
Here is a hint. There pretty much is no "T6 layer" because .... well T6 isn't associated with surface alloying stuff and for the Aluminum metal series, it typically isn't associated with superficial heating.
Typically, T6 is a specification of a heat-treatment that induces tiny precipitates from constituents that were initially in the 6061 or other aluminum alloy the day the substance was ""born" in the aluminum mill.
There is a lot of good informatin on Aluminum and many other things at this wonderful site: