A7003 합금의 환경친화적 압출공정을 위한 Mg 조성 및 공정비교 연구

최근 수송기계 경량화 추세에 부응하여 door impact beam, seat side rail 및 hood support와 같은 자동차 부품등에 Al-Mg-Zn계 중경질 A7003 합금소재의 적용이 검토되고 있는 실정이다. 그러나 이들 합금소재의 적용을 위해서는 제품의 용도와 특성을 만족함과 동시에 압출성이 높은 합금소재의 개발이 선행되어야 한다. 본 연구에서는 A7003 합금소재의 압출 성을 향상시키기 위하여 합금원소 첨가량이 미세조직, 압출성 및 기계적 특성에 미치는 영향을 조사하였다. Mg 조성 제어에 의해 기계적 강도의 저하없이 A7003 합금의 압출성을 향상시킬 수 있었다. 또한 MLCA 기법을 적용하여 A7003 합금중의 Mg 첨가량 및 빌렛가열정 변화에 따른 에너지 소비량 및 환경오염부하물질 배출량을 산정하였다. A7003 합금중 Mg의 첨가량을 제어하여도 압출재 생산에 소요되는 에너지의 소비량은 거의 같음을 확인하였으며 CO₂와 같은 대기오염물질을 저감시키기 위해서는 유도가열에 의한 빌렛가열공정의 적용이 가장 효과적임을 알 수 있었다.

A7003 alloy has characteristics of their excellent weldability, high corrosion resistance and superior plastic working however the broadening of application for the alloy has been hampered by the lower extrudability associated by Mg content. For improvement of extrudability and enhanced recovery efficiency during Al scrap recycling, it has been generally practiced to reduce Mg content in A7003 alloy. Therefore, it is necessary to investigate the influence of Mg content on mechanical strength and extrudability of A7003 alloy. For efficient material processing which has small amounts, material life cycle assessment(MLCA) is evaluated. The quantitative analysis of energy requirements and CO₂ emission for production of A7003 extruded bar are estimated with different Mg content and billet pre-heating process (heating source by light oil or LPG). In particular, the estimation of energy requirements was performed within shipping and gating range (except the mining and extraction stages) to investigate the influence of the variables on energy requirements and CO₂ emission in detail. As Mg content increased, the flow stress and the extrusion pressure for A7003 alloy increased. It has been thought that an increment in extrusion pressure with increasing Mg content is caused by the solid solution hardening of Mg atoms in the matrix and increment in volume fraction of intermetallic compound, Mg2Si. The extrudability and the tensile strength are equal to, or above that of conventional A7003 alloy even the content of Mg varied from 1.1wt.% to 0.5wt.%.alloy. This means that minimizing the content of Mg in A7003 alloy can enhance recovery efficiency during Al scrap recycling. It can be quoted that rather than Mg content energy source for billet heating is a prime factor to determine the atmospheric CO₂ emission