Zirconium The Impact Of The New Ultra-high-strength Aluminum Alloy Microstructure And Properties

In order to examine the effects of trace element Zr on aluminum alloys, the evolution of microstructure and mechanical properties of a new type super-high strength aluminum alloy 7A60 with various contents of element Zr was studied in this paper. Based on the product process, microstructures of the alloys under different states (as-cast, homogenized, forged, solution, aged) were systemically investigated by means of optical microscope and modern material research measures like SEM, TEM and DSC etc. Finally the influence of element Zr on fracture mechanism and strengthening mechanisms of Al-Zn-Mg-Cu aluminum alloys containing element Zr was discussed.The effects of element Zr connect with the morphologies. Usually there are different morphologies of zirconium even under a same state, so the. influence of zirconium was distinct, sometimes even contradictious. Although the most of element Zr solved as Zr atoms in the alloys under the as-cast state, the granularity is apparently various with different content of element Zr. The volume of element Zr increases, the mean diameter of grains decreases. When the content of Zr reaches 0.06wt%, the curve of granularity appears a peak, and then gently falls. When the content of Zr is over 0.12wt%, the granularity gradually increases with the Zr content again. When the ingots were homogenized, Zr atoms in matrix decompose, and precipitate as fine, dispersive A^Zr particles. The density of these particles is to be higher and the distribution to be more dispersive with the increase of Zr content. Some A^Zr particles can promote the precipitation of equilibrium phases when cooling in the furnace. During forging and solution heat treatment, AlaZr particles suppress the recovery and recrystallization behaviors. The high-density dislocations and elongated fibrous microstructures can be remained, which is improving the effect of deformation strengthening. In aging process, Zr atoms in solution slow the formation of GP regions because they joint with vacancies. Meanwhile AlsZr particles promote the nucleation and precipitation of n ' phase, which is greatlychanging the aging kinetics from double-peak strengthening to single-peak strengthening.Mechanical properties such as strength and elongation are significantly affected by the addition of element Zr. The strength increment can reach 416MPa/l%Zr. Results of SEM reveal that fracture mechanism accordingly converts from brittle-ductile fracture to pure ductile fracture with the increase of Zr content.Massive Al^Zr primary compounds have been found in the alloy with 0.16wt%Zr. These AlsZr are brittle compounds like intermetallics containing Fe or Si that do great harm to the properties. Several effective methods to avoid the formation of the massive A^Zr compounds were suggested.Taking account of the microstructure and properties, the preferable addition of element Zr in this experiment is 0.06~0.14wt%. This addition not only avoids the formation of AlsZr primary compounds, but also maintains beneficial effects on grain-refinement, resist-recrystallization behaviors. The performance of alloys remains at a higher level.