Polysiloxane hydraulic fluids

A hydraulic fluid composition comprising a polysiloxane compound and a non-halogenated diphosphonate compound, wherein the polysiloxane compound is represented by a compound of Formula 1:

• wherein:
• y is an integer selected from 1 to 40;
• R1, R2, R3, and R4 are each independently selected from the group consisting of C1-10alkyl, aryl, and C1-10alkylaryl;
• each R5 and each R6 is independently selected from the group consisting of C1-10alkyl, aryl, and C1-10alkylaryl;
• at least one of R1 to R4 or at least one of R5 and R6 of at least one of the y units is C1-10alkylaryl;
• and
• the polysiloxane compound has a mol % of aryl moieties of about 15 mol % to about 35 mol %, relative to silicon.