High phosphorous electroless nickel has poor salt spray life due to base metal porosity

we are the job plater and processing brake pistons in high phosphorous electroless nickel, we are facing problem of low salt spray because of base metal porosity. please advice how to overcome this problem.

Usually, High-phosphorous have better corrosion resistance than Low phosphorous. But your case, you may have metal porosity (i can't say, without seeing your sample.)

But I can give a suggestion (preliminary)
1, surface finish is correct (means either contamination or oil)
2, make sure your pre-treatment is correct (depends on your substrate, pretreatment will differ)
3, Bath composition is correct or not., (or whether you have tested by EDX or not) or simply saying I have high-phosphorous, and Ni/Hypophosphate ratio will be in the range of 0.3 to 0.5 (good)

FINALLY, (Main suggestion) coming to your problem
1, porosity have many reason: long time immersed in the bath (more than hour), TRY to keep the concentration same throughout the experiment and pH,
2, If you add surfactant (increase the surface adhesion between metal /ions, hence no porosity) like CTAB or SLS (in ppm level), you will get better results., Recent papers suggests.