Alloy Wheel Corrosion & Discolouration

The chief cause of complaint from customers over alloy wheels is discolouration, corrosion and flaking.

No warranty applies to corrosion or paint flaking due to damage caused by curbing or the use of chemical cleaners or any damage caused as a result of racing activity. No warranty applies to salt corrosion due to neglect of the wheels.

In other words you need to pay attention to what products you use when washing your van 
as some are so harsh they will damage it. In these cases its the manufacturer of the cleaning product that is responsible not the alloy wheel manufacturer 

Winter Wheels & Salt Corrosion 
Salt water causes the corrosion of aluminum creating aluminum oxide. The salt does not directly attack the aluminum, but causes an electrochemical attack like a catalyst that results in the corrosion. ... Al/Li alloys corrode fairly quickly while purealuminum corrodes much slower.
Alloy wheel manufacturers cannot change the laws of chemistry. If you get salt on your wheels you need to wash it off as soon as possible. 

Tips for protecting your wheels from corrosion 

• Wash often with a good brand of cleaner
• Avoid harsh or abrasive cleaners
• Use wheel protector such as Poorboys or Autoglym