The scale should be removed by acid pickling.  If it is not, the zinc will not react properly with the steel.

Hi Abdulwahab,

Although most standards insist on removing oxide scale on the metal surface prior to the galvanization process (see for example  ASTM A780, ASTM D6386 and ASTM D7803). That is because the oxide layer undermines the surface wettability with the molten zinc. However, this effect appears temporary and may be overcome by longer immersion times in the molten zinc. The article (below) claims that if the oxide layer is well adhered to the base metal surface, then its presence is not that bad after all and may be advantageous from the point of view of corrosion protection. They even suggest the possibility of galvanising corroded steel, without the usual surface preparation methods.

S.M.A. Shibli and R. Manu; Improvement of hot-dip zinc coating by enriching the inner layers with iron oxide; Applied Surface Science; Volume 252, Issue 8, 15 February 2006, Pages 3058–3064.

the scale would prevent the bonding

it defeats the purpose of galvanizing