铝为什么被誉为“会飞的金属”？

人们常把飞机比成银燕，其实，习机是用铝和铝合金做的．纯铝很软，人们在纯铝中加入4%铜与少量的镁产、锰、硅、铁等，制出了硬铝．由于硬铝既保持了密度小的特性，又克服了纯铝软的特点，因此硬铝很快就成了最重的一种合金．一架普通的飞机，差不多要用50万个硬铝做的铆钉，另外，飞机的外壳、机翼、机尾、螺旋桨、引擎的许多部件也是用硬铝做的．

在金属的家庭中，由于铝的密度小，使它得天独厚地能随飞机一起腾云驾雾，遨游高空，因此被誉为“会飞的金属”．

以前，这个“会飞的金属”，还只能飞翔在地球附近的高空，可是从1957年起，随着人造卫星与宇宙火箭一个个接连上天，铝就成了“飞天”的原材料，前苏联第一颗人造卫星的密封外壳与第二颗人造卫星的动物舱，以及球形容器都是铝合金做的．

本来，铝已经够轻的了，可是1958年以来又研制出了更轻的铝﹣泡沫铝，在泡沫铝的“肚子里”尽是氢气泡，放在水里，它会像木头一样浮起来，1m³的泡沫铝，只有178kg，而1m³的水有1000kg，另外泡沫铝能保温、隔音，不易锈蚀．目前用泡沫铝来做飞机与火箭是最理想的材料．

    The White House is an important historical building in the USA. It lies1the country's capital. Many people expect2see the palace with their own eyes.

    We3six months getting tickets to visit the White House. I was 4with excitement while we were waiting in the White House South Lawns. The first thing5interested me was the colorful flowers and green grass.

    Everything inside and outside was6kept in the white House. We went7many security checks(安检)8entering the building. In the east hallway9the first floor, I saw the pictures of past presidents on the walls. The10had over 2700 books. The Vermeil Room(金银屋) and China Room（瓷器屋） showed different11

    We walked upstairs to the State Floor. The East Room, the12in the White House, was the most wonderful in its size and furniture. This is the room where the president usually13the reporters. The Green, Blue and Red Rooms on the same floor got their names because of the 1414of the furniture and walls. These rooms are15having parties for state guests.