ActionMailer Problem

Hi, I wanted to send an attachment in mail. for testing , I have send png image attachement in mail. Mail delivery is completely working but the attachment in that mail show file name as “nonname” what should i do?? My code is:

class SendMail < ActionMailer::Base default :from => “XXXX@gmail.com

def welcome attachments[“adfd.txt”] = File.read(“#{Rails.root}/public/images/f.txt”)

 mail(:to => "XXX@gmail.com",
      :subject => "welcome mail").deliver

end

end