No you can't. Since when you archive an app, you get an .ipa file, or a XCArchive.
.ipa files are already compiled, and XCArchives have your compiled app in it, so you can't easily get the code from it.
But what I've tried to do with my own application is use Hopper Dissambler: http://www.hopperapp.com. It attempts to create "pseudocode" (from the executable) so you can kinda read it easier.