Попробуйте:
Option Explicit
Sub ArrayLoop()
Dim ArrList As Variant
Dim ArrItem As Variant
Dim Result As String
ArrList = Array("681120", "953160", "909420", "16300")
Result = ""
For Each ArrItem In ArrList
If Result = "" Then
Result = ArrItem
Else: Result = Result & "_" & ArrItem
End If
Next
End Sub