Study On The Microstructures And Mechanical Properties Of High-Strength And Heat-Resistant Al-Si-Cu-Mg Alloys

This paper is design a high strength and heat resistance Al-Si-Cu-Mg alloys with excellent comprehensive performance on the basis of ZL702A alloy for the requirement of high-power diesel engine. The effect of Cu, Mg, Si, Zn, Ti,Sr,RE addition on mechanical properties of Al-Si-Cu-Mg alloy were discussed. The effect of Cu on fluidity, linear contraction ratio and heat tearing of Al-7Si-xCu-0.3Mg (x=1.5～3.5wt%) alloys were measured and discussed. At last, solution treatment technology and aging process of alloy were studied. The main conclusion and results are as follows:Si, Cu, Mg and Zn had different effects on properties of Al-Si-Cu-Mg alloys. As the tensile strength, the influence of elements order is Si＞Mg＞Cu＞Zn,but as the elongation, the influence of elements order is Cu>Si>Mg>Zn. With the increase of the content of four alloy elements, the tensile strength of the alloy increased and elongation decreased. When 0.2wt%Ti element added to Al-Si-Cu-Mg alloy, make grain refinement to a (Al),and the mechanical properties of alloy significantly improved. Sr modification had better effects on the mechanical properties of alloys than RE modification. The optimized technology of Sr modification was 0.03 wt%Sr addition. The optimized components of high-strength heat-resistant Al-Si alloy was 7.0wt%,2.5wt%Cu,0.3wt%Mg,0.5wt%Zn,0.2wt%Mn,0.4wt%Ti and 0.03wt%Sr。With the increase of the content of Cu, the crystallization temperature interval of Al-7Si-xCu-0.3Mg alloy increased. When the content of Cu increased from 1.5wt.%to 3.5wt.%, the crystallization temperature interval of the alloy increased 25℃. When alloy solidification,θphase(Al2Cu) significantly increased, theα(Al) dendrite skeleton network was formed easily which made the fluidity of the alloy decreased, the linear shrinkage and hotness tendency increased. DSC research shows:the temperature of eutectic transformation was 510℃for Al-7Si-2.5Cu-0.3Mg-0.5Zn-0.2Mn alloy. Eutectic phase was mainly composed ofθphase (Al2Cu) and Q phase (Al5Si8Cu2Mg6). And after 500℃×4h solution treatment, Copper-rich phase of the allay was completely dissolved, then the start melting temperature was up to 535℃, bipolar solution treatment could improve the mechanical properties of the alloy. During aging treatment at 175～200℃in alloy, the hardening curves of the alloy presented apparent double peaks, because that 0 phase and 0 phase restrained dislocation motion and there was apparent time interal during the two phase transition.Using 500℃×4h+525℃×14h+165℃×4h heat treatment process can require the best mechanical properties for Al-7Si-2.5Cu-0.3Mg-0.5Zn-0.2Mn alloy,in room temperatureσb≥340MPa,δ5≥4.0%,200℃σb≥250MPa,δ5≥10.0%。...