【摘要】 用自制的实验装置研究了富铈稀土、镧和钇加入量对Al-5％Cu合金凝固过程准固态强度、强度增长率、准固态区间、断裂应变、裂纹总长度及最大裂纹宽度的影响。结果表明:稀土能不同程度地降低合金的准固相线温度,缩小准固态区,使准固态强度增长率和准固态后期的强度提高,减小裂纹总长度和裂纹最大宽度,降低合金的热裂倾向性。分析表明,热裂倾向性降低主要是由于稀土的加入缩小了合金的准固态区间。更多还原

【Abstract】 In this paper the influence of the additions of mischmetal, lanthanum or yttriumon the mechanical properties of quasi-solid and solid-liquid coexisting zone of Al-5%Cu alloy during solidification is investigated with self-made apparatuses, the mea-sured values of minimum stress and strain are 1.3 g/mm~2 and 0.03% respectively.The influence of the additions of these rare earths on the tendency of hot crac-king for the alloy is also studied with the hot crack ring device. Results show thatan addition of the rare earths will lower the quasi-solidus temperature, narrow therange of quasi-solid and raise the rate of strength increase and the strength in thelater stage of quasi-solid The more the rare earths is added the greater this effectwould be, for instance, with 0.5% addition of mischmetal, the failure strain in thelater stage of quasi-solid will increase considerably. An addition of rare earths willalso decrease the maximum crack width and the accumlative crack length, and reducethe tendency of hot cracking for the alloy. Yttrium is able to improve markedlythe mechanical properties of the allpy, but decrease the tendency of hot crackingonly slightly. Lanthanum is able to improve the mechanical properties only slightly,but decrease the tendency of hot cracking markedly. From these facts it seemsthat the magnitudes of the strength and failure strain in the quasi-solid are not themain factors influencing the tendency of hot cracking. The authors further ana-lyze the influence of the range of quasi-solid and the rate of strength increase onconcentrated strain in hot spot, which is considered as a main factor for the hotcracking formation. The results also indicate that the greater the range of quasi-solid, the longer the duration of the concentrated strain, so that the alloy withnarrow range of quasi-solid shows a less tendency of hot cracking; while thegreater the rate of strength increase, the greater the concentrated strain at the centreof hot spot, so that the alloy with greater rate of strength increase shows a greatertendency of hot cracking. The rare earths have a mixed effect on the tendencyof hot cracking for the alloy, since they can narrow the range of quasi-solid soas to decrease the concentrated strain, i.e., the formation of hot cracking, expe-rimental results are in agreement with the above analysis.更多还原