Goldbridge,
I don't have time to check it, but f2, I think, should be a file path or a file object - not a folder object:
fileObj.copy (target)
target - A string with the URI path to the target location, or a File object that references
the target location.
Copies this objects referenced file to the specified target location. Resolves any aliases to find the source file. If a file exists at the target location, it is overwritten.
So it should be:
var myText = "save this";
f1=new File("~/Desktop/images/1.txt");
f1.open("w");
f1.write(myText);
f1.close();
// I assume that aaa folder already exists
f2=new Folder("~/Desktop/images/aaa");
f1.copy("~/Desktop/Images/aaa/1.txt");
Kasyan