Aluminum makers won a discount on power rates.

The Bonneville Power Administration said it cut its electricity rates for the six producers through mid-1986. The 20% discount, to about 1.88 cents per kilowatt-hour, means that the companies--Aluminum Co. of America, Atlantic Richfield, Commonwealth, Intalco, Reynolds Metals and Kaiser--will probably maintain production at near-current levels for the duration of the agreement.