Solidification Behavior Of The Interface Of Aluminum Clad Magnesium Bimetal Composite Materials

Aluminum-magnesium composites are widely used in industrial production,including automotive steering wheel and engine parts,aircraft wings and skins,and shock-absorbing laminates for military armored vehicles.However,the poor connection ability and cold deformability of magnesium alloys and the existence of interfacial brittle intermetallic compounds restrict the development of magnesium-aluminum composites.Therefore,it is necessary to carry out research to solve these three problems.The AZ91/6061 composite ingot was prepared by a milder method of solid-liquid composite with less heat exchange.AZ91 was made into semi-solid billet by SIMA method to improve its intensity.The effects of various process parameters on the interface structure and semi-solid microstructure were optimized,and the thermodynamics and kinetic calculations of interface phase growth were discussed.The following conclusions are obtained:When the composite ingot was prepared by the solid-liquid composite method of melting casting 6061 into the semi-solid AZ91 billet side,the rivet was preferably used to fix the solid core.Based on the sensitivity of the AZ91 semi-solid structure to the temperature,the semi-solid billet was not preheated,and the ingot was ingot,the inner and outer diameter ratio of the ingot was 22:36,and then the composite ingot with obvious intermediate semi-solid structure was obtained.Other conditions were determined,as the temperature of the outer melt increased,the interface width was widened,and the interface area was divided into three distinct layers.From the inside to the outside,the interface sequentially formed eutectic(δ-Mg+Al₁₂Mg₁₇),Al₁₂Mg₁₇7 and Al₃Mg₂ by OM,XRD,EPMA,etc.The optimum outer melt temperature was 760℃,and the brittle hard zone I（Al₃Mg₂）had the smallest thickness ratio.By analyzing the influence of different casting temperatures on the interface structure,it was found the concentrations of Mg,Al,Si,Cu and Mn gradually decreased from one side of the substrate to the other side,and the Zn element shows speciality.At a relatively low temperature（740℃Or 760℃）,Zn diffusion distance was short,due to short-term fusion,the Zn content at the interface was slightly higher than the magnesium matrix.At high casting temperature（780℃to 820℃）,long-distance diffusion occured,the Zn content gradually less from the magnesium side to the aluminum side.For the semi-solid structure close to the interface,from 740℃to 820℃,it underwent the changes of hemi-crystallization,rounding and coarsening dendrites;the Zn content at the grain boundary of the solid phase particles near the interface,from the interface to the magnesium side,the Zn content intensity corresponds to low temperature,medium temperature and high temperature,respectively,showing a tendency to decrease,smooth and increase.Through thermodynamics and kinetic of interface phase growth calculations,it was concluded that Al₁₂Mg₁₇7 was formed earlier than Al₃Mg₂,Al₁₂Mg₁₇ phase average width prediction modelX_mean=0.091584exp（-5648.74902/T）^0.5had good precision,It was further determined that the formation mechanism of the interface layer was a combination of the fusion reaction and the diffusion reaction.Figure 34;Table 3;Reference 98.