Steps to export model file in AX
PS C:\> set-Location "C:\Program Files\Microsoft Dynamics AX\60\Server\MicrosoftDynamicsAX\bin"
PS C:\Program Files\Microsoft Dynamics AX\60\Server\MicrosoftDynamicsAX\bin> axutil.exe export /file:C:\USR.axmodel /model:Learn
PS C:\> set-Location "C:\Program Files\Microsoft Dynamics AX\60\Server\MicrosoftDynamicsAX\bin"
PS C:\Program Files\Microsoft Dynamics AX\60\Server\MicrosoftDynamicsAX\bin> axutil.exe export /file:C:\USR.axmodel /model:Learn