A corrosion-inhibiting composition for application to a metal substrate, such as aluminum or steel, and in connection with a paint, and the synthesis of the composition. The active inhibitor constituent of the composition can be selected from the group consisting of 2,5-dimercapto-1,3,4 thiadiazole (DMTD), 2,4-dimercapto-s-triazolo-[4,3-b]-1,3-4-thiadiazole, trithiocyanuric acid (TMT), and derivatives of DMTD and TMT, including various N-- or S-- and N, N--, S-- and N--,S-substituted derivatives of DMTD, including salts of DMTD of the general formula: M(DMTD).sub.n, where n=1,2 or 3, and M is a metal cation and preferably M=Zn(II), Bi(III), Co(II), Ni(II), Cd(II), Pb(II), Ag(I), Sb(III), Cu(II), Li(I), Ca(II), Sr(II), Mg(II), La(III), Ce(III), Pr(III), Al(III) or Zr(IV). DMTD, TMT, and their derivatives may also be combined with phosphates, molybdates, borates, silicates, tungstates, phosphotungstates, phosphomolybdates, cyanamides, carbonates, SiO.sub.2 and mixtures thereof.