To access the excel graphs axis, if I remember correctly, you can obtain the axis collection from a chart property, and then via Item with the index (1 -> y, 2 -> x ???) get the axis you want. On that reference you can set the properties of the axis as you would do in excel.
If your issue is just about exporting the image, you can obtain the image of the graph by a method (invoke node) of the indicator and then save it as bmp or png.
Felix