Microstructure And Mechanical Properties Of Mg/Al Composite Laminates Fabricated By Extrusion

Mg/Al laminate composites that combine the advantages of Mg alloy and Al alloy are effective to excellent properties, and thus, find great potential applications. In the present study, two well bonded Mg/Al laminate, Mg AZ31/Al 7050 laminate with the aim to harden Mg alloy and Al 1100/Mg ZK60 with the aim to increase ductility, were successfully fabricated by extrusion directly from the as-cast alloys. Microstructure and mechanical behavior of the composite laminates were systematically studied using EBSD, optical microscopy and SEM. The relationship between the composite and its constituent was also addressed. Several conclusions are reached as follow:(1) High quality AZ31/7050 and 1100/ZK60 composite were prepared by co-extrusion Mg/Al bimetal billets from the as-cast condition. A good bonding between Mg/Al layer is obtained. The thickness of transition layer is in a range of 5-10 microns. The layers in Mg/Al composite can be tailored by control the initial bimetal billets. The layers in composite is straight and uniform.(2) In the AZ31/7050 composite extruded at 470 oC, the Mg layer contains high fraction of recrystallized structure and a little deformed one. A bimodal structure containing both the fine and coarse grains exists in Mg layer. The Al layer contains a a fiber structure with a small fraction of equaixed grains. The Mg layer has a typical extrusion texture with most basal poles parallel to the ND(85%) and a small fraction of that parallel to the TD(15%). A high fraction of S(58.3%), Cube(18.9%)and Goss component exist in Al layer. Brass and Copper are hardly detected.(3) In the AZ31/7050 composite extruded at 470 oC, the high strength 7050 Al layer effectively enhances the strength of composite. Compared to the yield strength of Mg layer, a 40.2% fraction of Al layer improve the yield strength from 150 MPa to 300 MPa with an increase of density by 20%. Annealing will result in the drop of yield strength, while an increasing of elongation from 1.5% to 5.4%. After annealing, the yield strength of Mg layer hardly change, while that of Al layer drops greatly. Increasing the annealing temperature further reduces the strength of Al layer. The rule of mixtures for yield strength can work well for yield strength of Mg/Al composite, while does not work for ultimate strength. The main reason lies in that the composite fails before both the Al and Mg component get to its ultimate strength..(4) In both the 3-layered and 7-layered 1100/ZK60 composite, there is bimodal grain structure in Mg layer and a fiber structure in Al layer. A high fraction fine grains exists in Al layers and this fraction is higher in 7-layered plate than in 3-layered plate. The Mg layer in 3-layered plate contains a strong basal texture with basal poles parallel to the ND, while a double peaked basal poles along the ED in 7-layered plate. There is a similar texture in both Al layer in 3-layered plate and 7-layered plate, A high fraction of copper, Brass and Cube component exist and low fraction of Goss and S. However, the maximum intensity of texture in 3-layered plate is more weak. After annealing, the fraction of recrystallized grains in Mg layer increases. The texture hardly changes after annealing..(5) The 3-layered 1100/ZK60 plate has a similar yield strength to that of 7-layered one(138 MPa), but much higher elongation(17.4%)...