Steel V Aluminium

Subject: 
Salt Spray Evaluation of Varied Substrate Pretreatment Combinations Under 954-Line Polyester Powder Coating

Summary:
Three types of substrate-pretreatment combinations were evaluated for corrosion resistance and adhesion properties under 54-Line Top Coat. The test cycle ran for 1000 hours.

The best performing combination was the mill finished aluminium with chromate conversion coating. After 1000 hours saltspray, the Aluminium tubes in this category show nil corrosion and excellent adhesion.

After 1000 hours, the galvanised steel substrate and Prepsol wipe showed complete loss of adhesion on the scribe lines.

Sandblasted black steel substrate performed poorly for resistance to corrosion, showing rusting after 240 hours and singns of undercreep on the scribe lines.

Test Details

• 5% =Neutral Saltpray to ASTM B117
  Rating Intervals taken 240,500,750 and 1000 hours
  Tested were:
• Mill finished aluminium with Chromate coating on tubes.
  Galvanised Steel - Prepsol Wipe tubes
  Sand Blasted Black Steel Tubes

Adhesion Test Results after 1000 hours:

                                                                              Rating 10=Execellent. 1= Poor

Mill Finish Aluminium - Chromat Conversion            10 Rating

Galvanised Steel - Prepsol Wipe                               2-4 Rating

Sand Blasted Black Steel                                          Not Tested

Mill finished alumiuium with Chromate Conversion Coating (3 tubes #1,#2 & #3)

  240 Hours - Tube appearance = excellent, No rusting, No blistering and No undercreep
  500 Hours - Tube appearance = excellent, No rusting, No blistering and No undercreep
  750 Hours - Tube appearance = excellent, No rusting, No blistering and No undercreep
1000 Hours - Tube appearance = excellent, No rusting, No blistering and No undercreep
                    (No loss of adhesion on the scribe)

Galvanised Steel - Prepsol Wipe using (3 tubes #4,#5 & #6)

240 Hours - Tube appearance = very good (some rust staining). A very small amount of rust visible on scribe
500 Hours - Tube appearance = very good. Undercreep and blistering on all six ends.  A very small amount        of rust visable on the scribe.
750 Hours - Tube appearance = good. Undercreep and blistering at all six ends, approx 10mm. No blistering or undercreep on scribe.
1000 hours - Tube appearance = good. Blistering and undercreep at the ends of the tube and some on the face. (All tubes had severe adhesion loss when rated on scribe)

Black Steel Sand blasted (3 tubes #7,#8 & #9)

240 Hours - Tube appearance = poor. Spot rusting along whole length. Severe rusting along scribe approx 1-1.5mm undercreep from scribe.
500 Hours - Tube appearance = very poor. Spot rusting along whole length, rust staining. Approx 3mm undercreep on scribe.
750 Hours - Tubes removed after 750 hours. Approx 5mm undercreep on scribe.
1000 Hours - Not rated