Polycrystalline Pt thin films of different thicknesses (0-75 nm) were introduced using magnetron sputtering in Pb(Zr0.52Ti0.48)O3 (PZT, 400 nm in thickness)/Pt/Ni multiferroic film heterostructures, aimed at optimizing the transfer efficiency of magnetostrictive strain from the bottom Ni foil to the top PZT film and thus the direct magnetoelectric (ME) coupling. The ME voltage coefficient α E31 was directly measured, while the strain transfer efficiency k was obtained by combined experimental and theoretical analysis. At the optimum Pt-thickness of 30 nm, the polycrystalline film heterostructure shows the largest α E31 of 772 mV cm − 1 Oe − 1 at a low dc magnetic bias field of 86 Oe, as well as the highest k of 83% that is comparable to that in epitaxial quasi-2-2 film heterostructures.