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Will porosity of aluminium lead to blisters of pin size?

WE ARE PLATING CADMIUM PLATING OVER ALUMINIUM AND ALUMINIUM DIE CASTING USING ELECTROLESS AS UNDERCOAT. WE ARE USING 6061 AND 7075 ALUMINIUM

MATERIAL. 6061 MATERIAL COMES FOR PLATING AS EXTRUSION . WE ARE FACING PROBLEM OF BLISTERS AFTER OVEN TEST. BLISTERS THAT WE OBSERVE ARE A PIN HOLE SIZE. WE HAVE NOT OBSERVED BLISTERS BIGGER IN SIZE. WE HAVE TESTED MATERIAL FOR POROSITY AND MICROPOROSITY OBSERVED WITH THE MATERIAL. CAN YOU PUT YOUR SUGGESTIONS ON THIS WHETHER POROSITY WILL LEAD TO BLISTERS AND HOW TO AVOID?

OUR CLEANING CYCLE FOR COMPONENT IS DEGREASING (TCE), SOAK CLEAN, RINSE, DESMUTTING (HNO3 95% + 5 %HF ) +RINSE. ZINCATING( CMP-ALBOND DIP),RINSE,80% HNO3 ( STRIP),RINSE,ZINCATING,RINSE,ELECTROLESS NICKEL 15 MIN. MID PHOS, RINSE, CADMIUM PLATING 40 MIN. RINSE, O.5 % HNO3, O.G. PASSIVATION, RINSE, RINSE, DRY.

THANKS,

KAMLESH BHATT
plating manager - PUNE, MAHARASTRA, INDIA
February 20, 2009