问题 问答题

请以Al-4.5%Cu合金为例,说明130℃时效过程(组织转变)及其性能(硬度)变化。

答案

参考答案:铝合金淬火后得到过饱和固溶体,之后加热保温,固溶体内会依次析出GP区、θ"、θ’、θ相。GP区的形成会使材料的硬度增加(第一个时效峰),长时间时效,GP区溶解,硬度下降。θ"的形成使得硬度继续增加(第二个时效峰)。当θ"全部溶解转化为θ’和θ’转化为θ后,硬度开始下降。

其中,α平衡、θ为平衡相;GP区、θ"、θ’为亚稳相。

阅读理解

When I was a boy growing up in New Jersey in the 1960s, we had a milkman delivering milk to our doorstep. His name was Mr. Basille. He wore a white cap and drove a white truck.

Of course, he delivered (分发) more than milk. There was cheese, eggs and so on. If we needed to change our order, my mother would write a note — “Please add a bottle of buttermilk next delivery”. Then she put the note and the empty bottles into the milk box. The next day, the buttermilk would magically appear.

There was also a close relationship between families and their milkmen. Mr. Basille even had a key to our house, for those times when it was so cold outside that we put the box in the house, so that the milk wouldn’t freeze. And I remember Mr. Basille from time to time taking a break at our kitchen table, having a cup of tea and telling stories about his delivery.

I am sad that there is no home milk delivery today. Big companies produce cheaper milk, and milk is for sale everywhere. People may not need the milkman anymore.

Recently, I saw an old milk box in the countryside and it brought back my childhood memories. I took it home and put it outside the door. My son’s friends always ask what it is. So I start telling stories of my boyhood, and of the milkman who brought us friendship with his milk.

小题1:The milkman delivered milk to family _____ in the old days.

A.by car

B.by bike

C.on foot

D.by truck小题2:The writer’s mother put the note _____.

A.into the bottles

B.into the milk box

C.in the kitchen

D.in front of the door小题3:The writer brought back home an old milk box because he _____.

A.missed the good old days

B.wanted to tell funny stories

C.needed it for his milk bottle

D.wanted to give it to the milkman

单项选择题