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Temperature dependences of the contact angle ͑T͒ between ͑i͒ specially grown tilt grain boundaries ͑GBs͒ in Al and the Zn-rich melt; ͑ii͒ tilt GBs in Zn and the Al-rich melt; and ͑iii͒ tilt GBs in Zn and the Al-based solid solution ͑Al͒Љ were measured using scanning electron microscopy and light microscopy. decreases with increasing T in all cases and reaches zero ͑complete wetting͒ at a certain temperature T w in cases ͑i͒ and ͑ii͒. The wetting transformation for Al GBs is discontinuous ͑first order͒: ͑T͒ dependence is convex, d / dT has a break at T w , and ϳ͓͑T − T w ͒ / T w ͔ 1/2 . The wetting transformation for Zn GBs is continuous: ͑T͒ dependence is concave, d / dT is continuous at T w , and ϳ͓͑T − T w ͒ / T w ͔ 3/2 . For the Zn GBs in contact with a second solid phase ͑Al͒Љ, ͑T͒ dependence is concave and ϳ͓͑T − T w ͒ / T w ͔ 3/2 for the extrapolated T w . The observed change from the discontinuous wetting transition for GBs in a metal with a higher melting point ͑Al͒ to the continuous one for GBs in a metal with a lower melting point ͑Zn͒ is explained using the approach proposed in ͓Pandit et al., Phys. Rev. B 26, 5112 ͑1982͔͒. The validity of this approach and critical exponent of 3/2 may indicate that GB wetting in the Zn-rich alloys is governed by the long-range forces.