URL Rewrite Not working while manually typing url in browser.

Hi,

i am doing with url re-write from aspx to .html
This is working fine when i click a link
For example when i click on a link "AboutUs.aspx" the url is re-write is "about.html"
but when i type manually in browser http://mysite.com/AboutUs.aspx it is not re-write to "about.html"

in global.aspx
routes.MapPageRoute("AboutUs","about.html", "~/AboutUs.aspx");

in web.config

<rule name="AboutUs">
<match url="(.*)about.html$" />
<action type="Rewrite" url="AboutUs.aspx" />
</rule>

is there any thing else i need to configure.
how can i resolve this, by typing url in browser.