As stated in Xanathar's Guide:
Adamantine is an ultrahard metal found in meteorites and extraordinary mineral veins. In addition to being used to craft adamantine armor, the metal is also used for weapons. Melee weapons and ammunition made of or coated with adamantine are unusually effective when used to break objects. Whenever an adamantine weapon or piece of ammunition hits an object, the hit is a critical hit.
Armorer's Arcane Armor and 14th Lv Arcane Propulsion Armor Infusion states:
Each model includes a special weapon. When you attack with that weapon, you can add your Intelligence modifier, instead of Strength or Dexterity, to the attack and damage rolls.
Thunder Gauntlets. Each of the armor's gauntlets counts as a simple melee weapon while you aren't holding anything in it, and it deals 1d8 thunder damage on a hit. A creature hit by the gauntlet has disadvantage on attack rolls against targets other than you until the start of your next turn, as the armor magically emits a distracting pulse when the creature attacks someone else.
Lightning Launcher: A gemlike node appears on one of your armored fists or on the chest (your choice). It counts as a simple ranged weapon, with a normal range of 90 feet and a long range of 300 feet, and it deals 1d6 lightning damage on a hit. Once on each of your turns when you hit a creature with it, you can deal an extra 1d6 lightning damage to that target.
14th Lv Arcane Propulsion Armor: The armor includes gauntlets, each of which is a magic melee weapon that can be wielded only when the hand is holding nothing. The wearer is proficient with the gauntlets, and each one deals 1d8 force damage on a hit and has the thrown property, with a normal range of 20 feet and a long range of 60 feet. When thrown, the gauntlet detaches and flies at the attack's target, then immediately returns to the wearer and reattaches.
Lightning Launcher was never specified that it fires projectiles but safe to say Adamatine's auto-crit-on-hit should not work for it. But however does any armor of Adamantine as an Armorer's Arcane Armor now qualifies as both weapon and armor or is it separate (all but gauntlets is armor and the gauntlets the weapon)? Are the Thunder Gauntlets and Arcane Propulsion Armor (Rocket Punch) allowed to have the auto-crit-on-hit that adamantine weapons do?