qw doesn't perform any interpolation: anything inside a qw is interpreted as litteral characters (with two minor exceptions: \\ and \delimiter). That's why you got this output: inside a qw, @array1 is no more special than Jan. Try this:

@array2 = (@array1, qw(Jan Feb Mar));
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Alternatively, you could use push, like so:

my @array2 = @array1;
push @array2, qw(Jan Feb Mar);
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