| Aluminum is one of the most abundant metal elements in the earth's crust.Aluminum alloy is a light alloy with a low density.It is often used in the fields of automobile transportation,aerospace industry,and defense equipment products.The A356 aluminum alloy studied in this paper is mainly used in casting aluminum alloy wheels,casting engine blocks and aviation castings.However,since the aluminum element is more active and the hardness of the A356 as-cast aluminum alloy is relatively low,in order to ensure the surface quality of aluminum alloy casting parts It is of great significance to improve its surface corrosion resistance,abrasion resistance and surface hardness,while improving its performance in various aspects,its thermal stability is also a part that cannot be ignored.The laser remelting technology has a simple process,and its rapid cooling characteristics increase the degree of subcooling,improve the surface structure state,and release defects such as surface pores,thereby improving the surface quality.Therefore,the laser remelting process is very suitable for the surface strengthening of A356 cast aluminum alloy.In this paper,under the same conditions,laser remelting surface treatments are performed with laser powers of 1000 W,1500W,and 2000 W,respectively.Corrosion resistance,abrasion resistance,surface hardness,and thermal stability of different process parameter samples are analyzed by various test methods.To provide relevant theoretical support for the surface laser remelting treatment of A356 cast aluminum alloy to promote the application of laser remelting technology in the field of aluminum alloy materials.The experimental results show that after the laser remelting,the remelted zone,heat affected zone,and substrate zone are obviously appeared on the surface of the A356as-cast aluminum alloy.The depth of the remelted zone increases significantly with the increase of laser power.Observation by optical microscope and scanning electron microscope revealed that the grain size in the remelted zone was significantly refined,the second phase in the remelted zone was diffusely distributed,the change in grain size in the heat affected zone was smaller,and the second phase in the heat affected zone was agglomerated.XRD and EDS analysis revealed that laser remelting did not cause phasetransformation.After subsequent high temperature annealing treatment,the metallographic structure of the sample remained stable,indicating that the laser remelted structure had very good thermal stability.In the mechanical property test,using micro-hardness test and nano-indentation experiment,it was found that the hardness of the second phase Al-Si eutectic phase is higher than that of the ?-Al phase.After the laser remelting treatment,the second phase is diffusely strengthened,which improves the surface hardness and uniformity.Through friction and wear experiments,it was found that the wear resistance of the remelted layer was improved due to the effects of fine grain strengthening and dispersion strengthening.The three-point bending test results show that the plasticity of the remelted layer increases significantly with the increase of laser power,and the metallurgical bonding ability between the surface strengthening layer and the substrate is very strong under the laser power of 1500 W and 2000 W.Using the electrochemical corrosion method,the polarization curve and impedance spectrum are analyzed.The results show that thermal residual stress is introduced after laser remelting,which improves the breakdown resistance of the oxide layer.The corrosion resistance in the 1000 W remelting zone is the best.The zone corrosion resistance is significantly improved in comparison. |
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