Development And Microstructure And Properties Of New High Strength And High Thermal Conductivity Cast Aluminum Alloy

With the rapid development of electronic information technology,the heat dissipation requirements of electronic devices will become higher and higher.Cast aluminum-silicon alloy not only has the characteristics of low density,corrosion resistance,easy processing and good formability,but also has higher cost performance compared with heat-dissipating materials such as gold,silver and copper.In this paper,from the aspects of alloying,die-casting process(die-casting temperature)and heat treatment system,we have developed high-strength and high-conductivity cast aluminum alloy with tensile strength resistance>300 MPa and thermal conductivity>170 W/m·K to meet 5G communication heat dissipation requirementsFirstly,this paper not only studied the influencing factors of the strength and thermal conductivity of cast aluminum alloy,but also analysed the effects of alloying,die casting process(die casting temperature)and thermal treatment on the microstructure and properties of cast aluminum alloy.The aluminum-silicon binary test shows that the Si phase is spherical when the Si element content is 10%.When the thermal conductivity is increased to 165.58 W/m·K,the alloy has good fluidity and the alloy composition is determined to be Al-10%Si.In the study of the effects of(Sr,Mg,Cu,Fe)elements on the performance of Al-10%Si,it was found that the addition of Sr modifier in Al-10%Si alloy can modify the eutectic silicon to enhance its mechanical properties,but reduce the thermal conductivity.The addition of Mg element increased the strength of Al-10%Si while lowering the thermal conductivity.To balance the two factors,determine the Mg content range from 0.25%to 0.35%.By studying the transformation rules of different Cu content,it is found that the mechanical properties of Al-10%Si are slightly improved,but the thermal conductivity is obviously decreased.Fe element is strictly controlled.Considering the cost,casting properties,mechanical properties and thermal conductivity of the alloy,al-10%si-0.3%mg-0.7%Fe was selected as the final composition.Then,three different die casting temperatures were selected for the die casting test while maintaining the other die casting parameters unchanged.X-ray non-destructive fluoroscopic monitoring,metallurgical microscope,scanning electron microscopy,energy spectrum analysis,thermal conductivity test and mechanical properties test were used to study the effect of die casting temperature on alloy properties,and studied the relationship between microstructure and properties of castings at different die casting temperatures.As the die casting temperature increases,the number of pores inside the casting increases,The size of a-solid solution in the microstructure increases,and the Chinese-shaped a-AlFeSi becomes needle-like ?-AlFeSi.The fracture changes from ductile fracture to brittle fracture,which deteriorates the toughness of the alloy.Both the strength and the thermal conductivity of the alloy achieved maximum values at a die-casting temperature of 650? which were 298 MPa(tensile strength),201 MPa(yield strength),and 143.23 W/m·K(thermal conductivity).Finally,three different artificial aging systems T1 were used to heat treat the castings at three die-casting temperatures,and the relationship between microstructure and properties under different aging systems and under different aging temperatures was studied.After three different aging treatments,the castings at each die-casting temperature showed a significant increase in thermal conductivity,the elongation showed different degrees of decline.When the die casting temperature is 650? and the aging system is 250?×10 min,the thermal conductivity of the alloy reaches a maximum of 165.14 W/m·K,and the corresponding mechanical properties are poor.Since the precipitation of Mg2Si is sufficient after long-term aging,the mechanical properties are maximized at the conventional heat treatment of 175?×6 h.The reasons for the poor mechanical properties of the high temperature aging treatment caused by the fracture morphology at 650? die-casting temperature are:blowhole and inclusion defects,and enrichment of the depleted Fe phase.The casting is heat treated by two two-stage aging processes,and the performance and thermal conductivity are improved relative to a single stage.The two-stage solution 1 is superior to the solution 2,and the tensile strength,yield strength and thermal conductivity simultaneously reach the optimum levels of 316 MPa,240 Mpa and 171.76 W/m·K,respectively.