According to the Official Handbook of the Marvel Universe, vibranium melts at 5,475°F.
Weapons: Defensor wears a suit composed of vibranium; an extraterrestrial metal brought to earth by a huge meteor and found only in the African kingdom of Wakanda and the Antarctic hidden jungle called the Savage Land. Wakandan vibranium has the ability to absorb all forms of energy in the electromagnetic spectrum, making it impervious to all radiation bombardments. Further, it has an extremely high melting point (5,475° Fahrenheit), making it extremely heat resistant, and an extremely low freezing point (crystallisation temperature of -395.4° F), making its tensile strength extraordinarily high at low temperatures. Vibranium is also able to absorb about 50% of inertial Impact (owing to an unusually tight molecular crystal lattice array in the form of a compound helix), preventing penetration by any ballistic projectile up to large anti-tank weaponry.
As found by @Valorum in the comments adamantium can be worked for a short period of time if it's kept above 1,500° Fahrenheit as stated in the Official Handbook of the Marvel Universe Vol 2. However, it also states it cannot be rearranged once it has solidified again implying that it has a one time melting point of 1,500° F.
Adamantium is created through the mixing of certain chemical resins whose composition is a United States government secret. For eight minutes after the resins are mixed, the Adamantium can be molded into a particular shape as long as it is kept at a temperature of 1,500 degrees Fahrenheit. After this brief period the process of creating Adamantium is completed. The extremely stable molecular structure of the Adamantium prevents it from being molded further, even if the temperature remains high enough to keep it in liquefied form. Only a device called a Molecular Rearranger can alter the form of hardened Adamantium.