| The Al-0.2Sc-0.04Zr and Al-0.2Sc-0.04Zr-0.01B alloys were prepared by melting appropriate amounts of Al-2.02Sc,Al-4.38Zr,Al-1.08B and 99.991wt.% (wt.%:mass percentage, the same as the following) high pure Al in air. The obtained alloys were homogenized at 645℃for 24h. Some homogenized alloy was extrused at 600℃. Tensile tests and electrical resistivity measurements of all alloys aged at different temperatures and times were carried out. Combining with the microstructure observations, the relationship between mechanical property, conductivity and aging condition were obtained. The effects of B addition and hot extrusion on the grain size, tensile properties and conductivity of Al-0.2Sc-0.04Zr (0.01 B) alloys were obtained and discussed.Mirostructure observation shows that the grain of all as-cast Al-0.2Sc-0.04Zr (0.01B) alloys is equiaxed. With the addition of B, the grain size of as-cast alloys increase from 300 to 400μm, which is apparently amaller than that of high pure Al (～mm). The Vickers microhardnesses of both as-cast and homogenized alloy hardness value are all about 20Hv. The hardness were not improved by B addition, but can be obviously improved hot extrusion.The ambient temperature tensile properties of Al-0.2Sc-0.04Zr(0.01B) alloys aged at different temperatures for 189 minutes show that mechanical properties depend strongly upon aging temperatures. After aging at the optimal aging temperature range of 300～380℃, the alloys own the maximum yield stressσ0.2 (-75MPa) and tensile strengthσb (～160 MPa), and the minimum elongationδ(15%). The addition of 0.01% B leads to the slight decrease ofσb,σ0.2 andδat above 330℃. Although hot extrusion has little effect on the strength levels of Al-Sc-Zr aged at 300～380℃, it can greatly improve the elongation. The rate of elongation improvement increases from 50～70% at ambient temperature to 30～50% at 300～380℃. In addition, the amount of improve ment on elongation will decrease with B addition. The ambient temperature tensile properties of Al-0.2Sc-0.04Zr(0.01B) alloys aged at different time for 330℃show that the optimal aging time is 189min. With further increasing aging time to one day, the strength of alloys remained unchanged. It suggests that the alloys have better thermal stability. In addition, the maximum aging strength of alloys drops about 5% when the alloys heated together with furnace during aging. In this situation, the optimal aging time decrease from 189min to 60 min while the optimal aging temperature is still 330℃.The electriccal resistivity p of Al-0.2Sc-0.04Zr (0.01B) increases linearly with increasing temperatures. However, an obvious abnormal increase of p of homogenized Al-0.2Sc-0.04Zr (0.01B) alloys is observed between 150 and 200℃; furthermore, this abnormal increase of p will disappear after aging at 330℃. It maybe associated with the structural transformation of grain boundary or the formation of precipitate near grain boundaries The aging at 330℃for 189 min can apparently decrease the p of Al-Sc-Zr and hot extrused Al-Sc-Zr-B alloys while it has liitle influence on the p of homogenized Al-Sc-Zr-B alloy. The B addtion in Al-Sc-Zr can decreases the p and increases the p-temperature coefficient of homogenized alloys at low temperatures.The results show that the optimal aging condition of Al-0.2Sc-0.04Zr (0.01B) alloys is 330℃for 189 min. Hot extrusion can greatly improve the elongation, although it has little effects on the maximum strength of alloys. The B addition can decrease the electrical reisistance of homogenized at low temperature. Nevertheless, it leads to a slight decrease of maximum strength of alloys aged at 300～380℃. In all, hot extrusion Al-0.2Sc-0.04Zr alloy has the best mechanical properties and conductivity. Its tensile strength is about 160MPa, and the conductivity at 20℃is 63% IACS. |
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