Study the Effect of Aluminum Variation on Hardness & Aluminum Loss in Zn-Al Alloy
The objective of this research is to study the hardness &aluminiumloss with percentage variation in Aluminium content added to zinc. As there is a method for coating known as Galfan is available, in which combination of 95%zinc and 5% Aluminium is used for protecting steel from corrosion.As there are not much details available about why this composition is used Zinc-5%Al, we are interested in study of effects of different composition of Aluminum with Zinc, so we study the effect by adding different composition 2.5%,4.5%,6.5%,8.5% & 11.5% Aluminum in Zinc, for this study we are using hot dip galvanizing process for studying this coating. Hot-dip galvanizing is widely used to improve the corrosion resistance of steel. To obtain high-quality coatings, some alloy elements are added to the zinc bath. Aluminum is one of the most important elements in galvanizing.Fe-Al phase diagram indicated thatα Fe is obtained between 1 to 11% of AluminiumGalfan alloy consist of 95% Zn and 5% Al. It was decided to study the effect of variation in Al content in ZincAluminium alloy .Also during melting of this alloy we wanted to observed loss of Al due to oxidation hence the above compositions were decided.
The Process Metallurgy of Zinc-Coated Steel Wire and Galfan ® Bath Management
The physical metallurgy and related process and product performance concepts for the zinc and zinc alloy hot dip coating of steel wire are briefly reviewed, and are illustrated with a detailed model of aluminum behavior in Galfan® process technology. Applications to hot dip bath management practices are set forth. Background The coating of iron and steel with zinc to improve corrosion resistance has been practiced in various forms for 260 years, and a thorough description of the numerous wire-related technologies has been compiled in the handbook Ferrous Wire. In general, the basic unalloyed zinc technologies may be grouped under the headings “hot dip galvanizing” and “electrogalvanizing”. Hot dip practice involves the passage of wire through a molten zinc bath, whereas electrogalvanizing involves electroplating. The galvanized steel coating may involve no further processing. Alternatively, it may be redrawn, or otherwise reworked, chromated or oiled. It is important to note that the success of these technologies and the serviceability of the final product depend substantially on prior conditioning of the wire. Critical annealing, cleaning and fluxing (in the case of hot dip) processes precede the coating step. Moreover, hot dip coatings are optimized by the maintenance of small additions of aluminum in the zinc bath and by “wiping” and quenching practices upon emergence from the bath. Modern, in depth presentations on zinc-based steel coating systems may be found in Zinc-Based Steel Coating Systems: Production and Performance. The physical metallurgical basis of zinc-coated steel has been recently reviewed in detail by Marder. It is practical and economical to apply a zinc alloy coating. Although traditional galvanized coatings with small (0.1%) aluminum compositions are the most popular, the most rapidly growing hot dip coating is made with the Galfan® process, wherein a Zn-5% Al coating is applied by hot dipping (all composition data in this paper are in % by weight). This paper reviews this process and presents a model for management of the aluminum content in the hot dip Galfan® bath. Galfan® Coating and Its Advantages In 1980, researchers at Centre de Recherches Métallurgiques, Liège, Belgium, under sponsorship of International Lead Zinc Research Organization Inc., developed the Galfan® coating system, involving a Zn-5%Al coating. Most commonly this coating involves a mischmetal addition, containing lanthanum and cerium additions up to about 0.5%. The Galfan® coating system has been widely licensed, and an extensive set of ASTM Standard Specifications pertain. Galfan® ingot for preparation of the hot dip bath is addressed by ASTM Designation B 750-99, and basic Galfan® coated carbon steel wire is addressed by ASTM Designation A 856/A 856M-98. The wire may be drawn after coating, and ASTM Designation A 764 (Type C) pertains to Galfan® coated and drawn mechanical spring wire. Additional specifications exist for strand (ASTM A 855/A 855M-98 and ASTM A 925-98), for chain link fence (ASTM A 817-94 and ASTM A 824-95), for gabions (ASTM A 974-97), and for steelreinforced aluminum conductors (ASTM B 232/B 232M-99 and ASTM B 401-99). The Zn-Al phase diagram is shown in Figure 1, and an eutectic point exists at a composition of 5% Al and at a temperature of 381°C. Thus, the Galfan® microstructure is largely that of a fine interspersion of the zinc terminal solid solution, ç, with up to 1.2 % aluminum, and the â phase, with at least 16.9% aluminum. The eutectic microstructure can be either lamellar or of a rod type, and a mixture of the two structures is shown in Figure 2. It is possible for the Galfan® microstructure to contain ç dendrites, and such dendrites may appear in conjunction with the rod type eutectic structure. The Galfan® microstructure is sensitive to cooling rate, with rapid cooling refining the eutectic structure and tending to eliminate ç dendrites. The additional of mischmetal to the Galfan® composition improves the fluidity and wetting characteristics of the molten alloy. The Galfan® coating provides improved corrosion resistance in comparison to a conventional galvanized coating, combining, in effect, the passive corrosion inhibition of aluminum oxidation with the active and passive effects of zinc. Representative data are shown in Figure 3. Beyond this, the eutectic structure is quite ductile, and Galfan® processing avoids the more brittle intermetallic phases that can exist in conventional galvanized coatings. Hence, Galfan® coated steel wire can be extensively redrawn and subjected to relatively severe wire forming operations. Adriaensen has discussed the advantages of Galfan® coated wire, vis-a-vis conventional galvanized wire, for steel springs and spring manufacturing, including consistency of spring length (associated with a decreased frictional interaction with coiling tools), and the good adherence of the Galfan® coating to organic coatings. Two Galfan® Processing Issues Molten Galfan® alloy is not compatible with the flux systems normally used with conventional galvanizing. While alternate fluxing arrangements are possible, this process limitation has led to wide usage of ”double dipping” processes wherein the Galfan® hot dip simply follows a conventional galvanizing hot dip, as schematically illustrated in Figure 4. In the double dip processing, the properly annealed, cleaned and fluxed steel acquires a galvanized coating in the first bath. This coating will generally include a series of iron-zinc intermetallic compounds at the iron-zinc interface, together with an overlay that is nearly pure zinc. The series of intermetallic compounds can be a source of coating brittleness. When the galvanized wire enters the second bath, containing molten Galfan®, the bath temperature will generally be high enough to melt or dissolve the essentially zinc galvanized overlay, and, furthermore, to transform the iron-zinc intermetallic layer into an aluminum-iron-zinc intermetallic. Upon emergence from the Galfan® bath a layer of essentially Galfan® alloy solidifies on top of the transformed aluminum-iron-zinc intermetallic layer. The above scenario is not one of steady-state, however, and the aluminum that enters into the aluminum-iron-zinc intermetallic layer inherently lowers the aluminum concentration in the Galfan® bath. Thus, Galfan® bath management requires the monitoring and management of the aluminum concentration. This paper sets forth, below, a process model that can be used by Galfan® processors to understand and undertake such bath management. A Model of Galfan® Bath Aluminum Concentration Let us start with the assumption that the process line is able to add Galfan® alloy to keep the bath mass constant in the face of withdrawal of alloy from the passage of wire. In such a case, the incremental depletion of aluminum in the bath, associated with an increment of wire coating, can be expressed as follows: (M) dC = I dA + (0.05) G dA C W dA, (1) where C is the aluminum concentration in the bath, dC is the incremental change in bath aluminum concentration, dA is the increment of wire surface coated, M is the mass of the bath, I is the mass of aluminum per unit of wire surface area in the transformed intermetallic layer, G is the net mass of Galfan® melt removed per unit of wire surface area, and W is the mass of the Galfan® overlay that solidifies per unit of wire surface area. The expression at the left in Equation (1) is simply the incremental mass of aluminum lost when an increment of wire surface area, dA, is coated in the Galfan® bath. The first expression on the right of equation (1) is the mass of aluminum that is lost to the transformed intermetallic layer when an increment of wire surface area is coated. The second expression on the right of Equation (1) is the amount of aluminum that is added to the bath per increment of wire surface area, assuming simultaneous bath replenishment with Galfan® alloy. The third expression on the right of Equation (1) is the aluminum lost per increment of wire surface area coated simply due to the solidification of the bath alloy on the emerging wire. Equation (1) can be usefully reorganized as follows: dC = ( X + YC) dA, (2)
Structure and properties of engineering alloys
1 Iron-Carbon Alloys I 2 Iron-Carbon Alloys II 3 Carbon Steels 4 Alloy Steels 5 Aluminum Alloys 6 Copper Alloys 7 Stainless Steels 8 Cast Irons 9 Tool Steels 10 Titanium Alloys 11 Nickel and Cobalt Alloys 12 Magnesium and Zinc Alloys 13 Refractory Alloys 14 Surface Hardening and Modification of Metals