PPGI is short for pre-painted galvanized steel, while PPGL is short for pre-painted galvalume steel. As the name suggests, PPGI uses galvanized sheets (with a layer of zinc coating) as base metal. While PPGL is with galvalume sheet as substrate, which is coated with 55% aluminum, 43.3% zinc, and 1.6% silicon. This is the main difference between PPGI and PPGL, which will further influence their features and applications.

As mentioned, both zinc coating and Al-Zn coating are used to protect the metal from rusting to prolong its service life. For the GI sheet, the base metal will be damaged when the zinc coating is all corroded. Generally, a galvanized sheet may last for 10 to 15 years. While aluminum and zinc alloy forms microscopic particle areas. The Zn-rich phase will corrode preferentially, while the Al-rich phase will corrode very slowly. So Al-Zn coating is more corrosion-resistant than zinc-coated steel sheet. According to data, the service life of PPGL is 3 times longer than that of PPGI. Below are some pictures for you.