January_2021_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | J A N U A R Y 2 0 2 1 2 5 specifications for T82 temper mandat- ed a minimum yield strength of 260 MPa after forming and aging, while retaining excellent ductility. The transformation of 6111 would consume both compa- nies and Ford for the next three years. John Hill and his team at Ford’s Research & Innovation Center were re- sponsible for structural bonding de- velopment. One of the fundamental manufacturing issues was the surviv- ability of the mill-applied surface pre- treatment through the PFHT process: If it did not survive, individual parts would require surface treatment af- ter heat treating, an expensive invest- ment in both capital and factory floor space. The second question was wheth- er parts could be heat treated without first washing off the stamping lubricant. They had positive answers to both is- sues by mid-December: PFHT could fit within the normal processing sequence, with the heat treat cycle as the only added step. KEY SPECS But in the beginning of the third quarter of 2010, the first order of business was to firm up material specifications for the new aluminum ABS. A cross-functional team from ma- terials engineering, stamping engi- neering, research & innovation, and product engineering received a two- pronged mandate from management: Deliver specifications tight enough to allow dual sourcing without trau- ma, and ensure scrap compatibility to maximize the value of stamping offal. This meant a strict harmonization of both material properties and chemical composition limits. Harmonizing the composition and mechanical proper- ty limits for 6111, 5754, and 5182 pro- gressed smoothly. The thin gauge outer skin alloys were the stumbling block, as Novelis and Alcoa were intent on sup- plying their own alloys. A glance at the registered chemical composition limits of the respective alloys explains their position (Table 1 and Fig. 2). Their starting position was that, at a minimum, Ford would have to seg- regate by alloy, if not by supplier. From Ford’s point of view, that position was clearly impossible. Harmonizing the composition of the skin ABS alloys be- came a focus of intense discussions be- tween Ford and its suppliers that would stretch for the next 12 months. The breakthrough came when Ford realized that all of the “low Cu” alloys actual- ly existed within a narrow overlapping compositional space that became the basis for the new “low Cu” specs. Mechanical property specifica- tions of 5xxx-O and 6xxx-T4 alloy sheet posed distinctly different challenges: For 5xxx, it was improving the measure- ment of uniform elongation and yield strength, while natural aging was the issue for 6xxx sheet. The specification concept was agreed on in third quar- ter 2011. However, the practical impli- cations for lot release by the mills and stock management at Ford were not fi- nalized until September 2014. The product and manufacturing teams were concentrating on the fast approaching X1 prototype build. The “Go Fast” X0 prototypes had provid- ed the product design team with some valuable information, such as improved correlation with computer-aided engi- neering (CAE), but the manufacturing team was starting from scratch. Nei- ther the stamping engineering nor body construction teams had any experience with thick gauge 6111. TABLE 1 — AA CHEMICAL COMPOSITION FOR VARIOUS 6XXX “LOW Cu” ALLOYS Alloy Date Si Fe Cu Mn Mg Cr Zn V Other 6005 1962 0.6 – 0.9 0.35 0.1 0.1 0.40 – 0.6 0.1 0.1 … 6005C 2005 0.40 – 0.9 0.35 0.35 0.5 0.40 – 0.8 0.3 0.25 … 0.50 Mn + Cr Ac120/6016 1977/1984 1.0 – 1.5 0.5 0.2 0.2 0.25 – 0.6 0.1 0.2 … 6014 1983 0.30 – 0.6 0.35 0.25 0.05 – 0.20 0.40 – 0.8 0.2 0.1 0.05 – 0.20 6022 1995 0.8 – 1.5 0.05 – 0.20 0.01 – 0.11 0.02 – 0.10 0.45 – 0.7 0.1 0.25 … 6451 2005 0.6 – 1.0 0.4 0.4 0.05 – 0.40 0.40 – 0.8 0.1 0.15 0.1 Fig. 2 — Graphic representation of Table 1.