1-D transient conduction explicit method

%I am trying to solve this problem but, I am just getting linear line as a result which is wrong.
% I tried to put if function beacause left wall i temperature prescribed and which is changing
%respect to the time. The right side is insulated. In this problem, I am using explicit method.

clear;
clc;
L= 0.152; %meter,  wall thickness
n= 10; %number of simulation nodes
Ti=80; % Deg F, Initial temperature of wall
% c=1; 

dx= L/n; %meter, node thickness
rho= 7801;
cp=473;
k=43;
alpha1= k/(rho*cp); %carbon steel
alpha2=0.00000525166; %nickel 
dt=0.1; %sec, fixed time step
t=0:dt:3;
nt=100;

if 0<=t<=1
    Ts1= 1500*t;
    Ts2= 80;
%  T0=400*ones(1,n);
%  T1=300*ones(1,n);
  for j=1:nt
    for i=2:n-1;
        T1(i)=Ts1(i)+alpha1*(Ts1(i+1)-2*Ts1(i)+Ts1(i-1));
    end
    T0=T1;
  end
elseif 1<t<=2
        Ts1=-1500*t;
        Ts2=80;
   for j=1:nt
    for i=2:n-1;
        T1(i)=Ts1(i)+alpha2*(Ts1(i+1)-2*Ts1(i)+Ts1(i-1));
    end
    T0=T1;
   end
else
     Ts1=0;
     Ts2=80;
   for j=1:nt
    for i=2:n-1;
        T1(i)=Ts1(i)+alpha2*(Ts1(i+1)-2*Ts1(i)+Ts1(i-1));
    end
    T0=T1;
   end
end
plot (T1)