Study On Microstructure And Properties Of Spray Deposition Si-Al Alloys

High-silicon aluminum alloy is very promising for aerospace electronic components,automobile engine, air condition and other applications which need lightweight, lowexpansion, high wear-resistant, but exsiting of coarse silicon obstacles this alloys’applications. Rapid solidification offers an effective way to solve this problem by refiningsilicon and promoting non-equilibrium phases to form.In this paper, a series of different Si contents Si-Al alloys（27%Si-Al、42%Si-Al、50%Si-Al） were prepared by double-nozzle scanning spray forming and hot isostaticpressing technology at Jiangsu Haoran Spray Forming Alloy Co., Ltd，with a size of Φ400mm×700mm. The microstructure and mechanical thermal properties of the alloys werestudied using optical microscopy, scanning electron microscopy, EDS, XRD, coefficient ofthermal expansion （CTE） and3-point tests. The friction and wear properties were studiedusing UMT-2testing system, Effect of Si contents, rotational speeds, temperature on frictionand wear properties were analyzed.The main conclusions in this work are summarized as follows:The results show that the as-deposited billet has an equiaxed and homogeneousstructure. With the rise of Si content, alloy solidification range has increased; the size ofsilicon crystal is larger, some Si particles bond together and show a network，the decrease ofthe coefficient thermal expansion is mainly because of this structure.The coefficient of thermal expansion （CTE） was measured, with temperatureincreasing, the CTE of the alloys increases gradually. The CTE of27%Si-Al、42%Si-Al、50%Si-Al alloys were14.76×10^-6/K、9.75×10^-6/K、9.29×10^-6/K from room temperatureto200℃. With the rise of Si content, the CTE decreases obviously.After hot isostatic process, with the rise of Si content, the tensile strength and bendingstrength decreased. The tensile strength of27%Si-Al、42%Si-Al、50%Si-Al are196MPa、143MPa、135MPa, and the bending strength of27%Si-Al、42%Si-Al、50%Si-Al are260MPa、232MPa、228MPa，the extensibility of27%Si-Al is9.5%.With the rise of Si content, the coefficient of friction shows a upward trend. The wornsurfaces of27%Si-Al alloy has occurred large numbers of plastic deformation at aluminummatrix phase, and a small amount of wear debris. The worn surfaces of42%Si-Al and50%Si-Al alloys has a phenomenon of a large number of primary Si fracture and fall off. Wear mechanism gradually changed from adhesive wear to abrasive wear. With the loadforce increasing, the coefficient of the friction shows a downward trend, it mostly becausewhen the load force increases, the primary Si broken and occurred three body abrasion wear.Effect of speed is mainly because the sub-surface deformation and surface temperaturechanged, it has significantly effect at27%Si-Al alloy. With the increasing of temperature,serious adhesive wear happened on27%Si-Al alloy surface, primary Si cannot play a goodsupporting role to resist the friction and wear. But on the surface of42%Si-Al and50%Si-Al alloys, the primary Si can resist the plastic deformation better than27%Si-Alalloy. Wear mechanism is adhesive wear and abrasive wear mixed together.