杂质Ca对Al-5Mg填充合金凝固组织及力学性能的影响

结合拉伸试验和冲击试验,采用SEM、EDS和XRD等分析方法研究了杂质元素Ca对铝镁焊接填充合金铸态凝固组织和力学性能的影响。结果表明,Ca元素的存在改变了合金相组成。当Ca小于0.28%,合金中晶界富集由块状(Ti,Cr)₂Ca(Al,Mg)₂₀金属间化合物相。当Ca大于等于0.28%时,块状(Ti,Cr)₂Ca(Al,Mg)₂₀相和不连续条状Al₂Ca相共同在晶界富集。随Ca含量的增加,合金中块状相和条状相尺寸逐渐增大,数量逐渐增加。合金抗拉强度随Ca元素的增加先升高再降低,Ca含量0.28%时抗拉强度达到峰值。Ca小于0.28%时,合金塑性和冲击韧性缓慢下降,当Ca大于0.28%时,条状Al₂Ca相和块状(Ti,Cr)₂Ca(Al,Mg)₂₀相在晶界共存,低应力下两相破裂成为裂纹源,Al₂Ca硬脆相削弱了晶间结合强度,合金塑韧性大幅下降。合金拉伸或冲击断口由穿晶延性断裂(Ca<0.28%)转变为脆性断裂(Ca>0.28%)。Ca含量0.28%为合金韧脆转变点。

Effect of Ca impurity on microstructures and mechanical properties of as-cast Al-5Mg filler metalsT

Effects of Ca impurity on microstructures and mechanical properties of Al-5Mg filler metals were investigated with SEM, EDS, XRD, tensile test and impact test. The results indicate that the phase composition of Al-5Mg alloy is changed by the Ca impurity. It is observed that block-like (Ti,Cr)₂Ca(Al,Mg)₂₀ phase distributed discontinuously along the grain boundaries when the Ca content is less than 0.28%. When the content of Ca is over 0.28%, bar-like Al₂Ca and block-like (Ti,Cr)₂Ca(Al,Mg)₂₀ combine together and distribute along the grain boundaries, and the amount and size of Ca-rich phase (both the bar-like and block-like) increase with the Ca content. Tensile strength of the Al-5Mg alloys increases firstly and then decreases with increasing Ca content, and the tensile strength gets to maximum value when the content of Ca is 0.28 wt%. The plasticity and fracture toughness decrease smoothly (Ca 0-0.28%) but then significantly (Ca>0.28%), and the tensile or impact fracture mode transform from the transgranular ductile fracture to the brittle cleavage fracture.